How to troubleshoot below mentioned two windows Update Issue.
1.  Windows Update utility checking for Updates but not populating "download and Install" list and running for infinite.
2.  Windows Update utility showing "Downloading and Installing" but there is no progress and running for infinite.
*****************************************************************************************************************************************************************
1. Symptom: Windows Update utility checking for Updates but not populating "download and Install" list.
The above mentioned symptom may be due to the "servicing corruption".
Solution ( Fixing servicing corruption):
Download the System Update Readiness Tool ( http://support.microsoft.com/?kbid=947821).
with the help of this tool we verifies the integrity of the following resources:

• Files that are located under the following directories:
  • %SYSTEMROOT%\Servicing\Packages
  • %SYSTEMROOT%\WinSxS\Manifests
• Registry data that is located under the following registry subkeys:
  • HKEY_LOCAL_MACHINE\Components
  • HKEY_LOCAL_MACHINE\Schema
  • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Component Based Servicing

It detects incorrect manifests, files, or registry data, it might replace the incorrect data with a corrected version.
However, the tool might be unable to fix all instances in which these errors occur.

The System Update Readiness Tool creates a log file that captures any issues that the tool found or fixed. The log file is located at the following location:

• %SYSTEMROOT%\Logs\CBS\CheckSUR.log
• %SYSTEMROOT%\Logs\CBS\CheckSUR.persist.log

Using the checkSUR report ( %SYSTEMROOT%\Logs\CBS\CheckSUR.log).
1. The System Update Readiness Tool has fixed all found errors, as in the example below:
Summary:
Seconds executed: 100
Found 10 errors
Fixed 10 errors

 2. If you get the Unavailable repair files message, this indicates that some of the inconsistent files found by the tool cannot be fixed as the correct versions of the replacement files are not carried by the tool. After this message appears, a list of the missing files follows.
Summary:
Seconds executed: 264
Found 3 errors
CBS MUM Missing Total Count: 3
Unavailable repair files:
servicing\packages\Package_for_KB958690_sc_0~31bf3856ad364e35~amd64~~6.0.1.6.mum
servicing\packages\Package_for_KB958690_sc~31bf3856ad364e35~amd64~~6.0.1.6.mum
servicing\packages\Package_for_KB958690~31bf3856ad364e35~amd64~~6.0.1.6.mum
servicing\packages\Package_for_KB958690_sc_0~31bf3856ad364e35~amd64~~6.0.1.6.cat
servicing\packages\Package_for_KB958690_sc~31bf3856ad364e35~amd64~~6.0.1.6.cat
servicing\packages\Package_for_KB958690~31bf3856ad364e35~amd64~~6.0.1.6.cat
winsxs\manifests\x86_microsoft-windows-servicingstack_31bf3856ad364e35_6.0.6002.18005_none_0b4ada54c46c45b0.manifest
winsxs\manifests\amd64_microsoft-windows-servicingstack_31bf3856ad364e35_6.0.6002.18005_none_676975d87cc9b6e6.manifest Steps to resolve the issue
a. Get the files required from other sources. The options available can be found in the "Options for obtaining files" section below.
b. Copy the files to %Windir%\Temp\CheckSUR directory of the corrupted computer following the subdirectory format as follows:
   i. All files of type *.mum and *.cat should be placed in the %windir%\Temp\CheckSUR\servicing packages directory
   ii. All files of type *.manifest should be placed in the *%windir%\Temp\CheckSUR\manifests* directory
For example:
Copy Package_for_KB958690_sc_0~31bf3856ad364e35~amd64~~6.0.1.6.mum to *%Windir%\Temp\CheckSUR \servicing\packages*
Copy x86_microsoft-windows-servicingstack_31bf3856ad364e35_6.0.6002.18005_none_0b4ada54c46c45b0.manifestto *%Windir%\Temp\CheckSUR \winsxs\manifests*
Note: Whenever you copy a .mum file, you must also copy the corresponding .cat file of the same name.
iii. Rerun the System Update Readiness tool.
3. If you get a Payload File Missing message, then the binary required is not available. This means that the issue is not fixed.
Summary:
Seconds executed: 100
Found 5 errors
Fix 2 errors
CSI Payload File Missing Total count: 5
Fix CSI Payload File Missing Total Count: 2
(f) CSI Payload File Missing 0x00000000 admparse.dll x86_microsoft-windows-ie-adminkitmostfiles_31bf3856ad364e35_6.0.6000.16386_none_abfb5fd109dad8b8 servicing_31bf3856ad364e35_6.0.6000.16386_none_23ddbf36a8a961bc
(f) CSI Payload File Missing 0x00000000 bootmgr x86_microsoft-windows-b..re-bootmanager-pcat_31bf3856ad364e35_6.0.6000.16386_none_c0f2f087b6457236
(fix) CSI Payload File Missing 0x00000000 bootmgr x86_microsoft-windows-b..re-bootmanager-pcat_31bf3856ad364e35_6.0.6000.16386_none_c0f2f087b6457236
(f) CSI Payload File Missing 0x00000000 winload.exe x86_microsoft-windows-b..environment-windows_31bf3856ad364e35_6.0.6000.16386_none_6701d52e8fdf8d45
(f) CSI Payload File Missing 0x00000000 setbcdlocale.dll x86_microsoft-windows-b..environment-windows_31bf3856ad364e35_6.0.6000.16386_none_6701d52e8fdf8d45
(f) CSI Payload File Missing 0x00000000 winresume.exe x86_microsoft-windows-b..environment-windows_31bf3856ad364e35_6.0.6000.16386_none_6701d52e8fdf8d45
(fix) CSI Payload File Missing 0x00000000 winresume.exe x86_microsoft-windows-b..environment-windows_31bf3856ad364e35_6.0.6000.16386_none_6701d52e8fdf8d45
 Steps to resolve this issue
   a. Find out which payload files are missing by looking at checkSUR.log. Identify any line that have (f) that is not followed by (fix). From the previous example the three payload files that are not fixed are:
(f) CSI Payload File Missing 0x00000000 winload.exe x86_microsoft-windows-b..environment-windows_31bf3856ad364e35_6.0.6000.16386_none_6701d52e8fdf8d45
(f) CSI Payload File Missing 0x00000000 setbcdlocale.dll x86_microsoft-windows-b..environment-windows_31bf3856ad364e35_6.0.6000.16386_none_6701d52e8fdf8d45
(f) CSI Payload File Missing 0x00000000 admparse.dll x86_microsoft-windows-ie-adminkitmostfiles_31bf3856ad364e35_6.0.6000.16386_none_abfb5fd109dad8b8 servicing_31bf3856ad364e35_6.0.6000.16386_none_23ddbf36a8a961bc

  b. Get the files required from other sources. The options available can be found in the "Options for obtaining files" section below.
Note:  Ensure the binary you get from matches the directory name mentioned on checkSUR.log. For the above example, the directory name is x86_microsoft-windows-ie-adminkitmostfiles_31bf3856ad364e35_6.0.6000.16386_none_abfb5fd109dad8b8
  c. Paste the files onto the proper subdirectory under c:\windows\winsxs.
Note: Please only paste the files that are needed. Replacing additional files may lead the system into an unserviceable state.
Before placing the files in the appropriate locations, you may need to grant yourself permissions to edit the folder's contents; below is a quick guide on how to achieve this.
  i. At an elevated command prompt: takeown /f Path_And_File_Name
  ii. Next, to grant administrators full access to the file: icacls Path_And_File_Name /GRANT ADMINISTRATOR:F
  iii. To replace the file with a known good copy: Copy Path_And_File_Name_Of_Source_File Path_And_File_Name_Of_Destination
4. Bad Pending.xml
The file used to record operations required during system reboot is bad or corruptedCheckSUR.log does not record this information, however this can be easily identified by checking if one of the registry values below exist:

1. HKLM\Software\Microsoft\Windows\CurrentVersion\SideBySide@CorruptPendingXml (REG_SZ)
2. HKLM\Software\Microsoft\Windows\CurrentVersion\SideBySide@CorruptPendingXmlIdentifiers (REG_SZ)

Important: In Windows 7 and Windows Server 2008 R2, a restart may help resolve the problem by removing the corrupted file. While users may see that some updates fail after a reboot, reinstalling the updates should now succeed. In Windows Vista and Windows Server 2008, no solution to recover this file exists

5. Bad Winner Keys
The registry used by the system to keep records of installed components is corrupt. CheckSUR.log does not record this information. However in Windows 7, this can be easily identified by checking if the registry value below exists:
   a. HKLM\Software\Microsoft\Windows\CurrentVersion\SideBySide@CorruptWinners (REG_SZ)
Note: For Windows Vista SP1 and higher, check this phrase on %windir%\logs\CBS\CBS.log or CBS.persist.log to identify winners key corruption "Install-map entry missing component key in populate".
CheckSUR does not currently repair this type of corruption. Attempting a System Restore or reinstalling the operating system is recommended.
Options for obtaining files :
 Obtain files from the update package
   a. Identify which update package you need to download. ( For Package_for_KB958690_sc_0~31bf3856ad364e35~amd64~~6.0.1.6.mum, the KB number is KB958690, the architecture version is amd64 (which is the same as x64) and the package version is 6.0.1.6.)
  b. Download the KB from Microsoft
rename it from .msu to .cab and we extract it to get our missing files
Most of the times at least 1 file can not be found so we have to rename the update.mum and update.cat to the missing file name and copying it to the checkSUR temporary directory
*********************************************************************************************************************************************************************************************
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
*********************************************************************************************************************************************************************************************
 2. Symptom: Windows Update utility showing "Downloading and Installing" but there is no progress and running for infinite.
This may be due to the windows update component corruption.
Solution ( Reset Windows Update Component ) :
Steps to reset windows Update Component
1. Stop below mentioned service:
  a. net stop bits
  b. net stop wuauserv
2. Delete the qmgr*.dat files.
Del "%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Downloader\qmgr*.dat"
   a. Rename the following folders to *.BAK:

• %systemroot%\SoftwareDistribution\DataStore ( Ren %systemroot%\SoftwareDistribution\DataStore *.bak)
• %systemroot%\SoftwareDistribution\Download (Ren %systemroot%\SoftwareDistribution\Download *.bak)
• %systemroot%\system32\catroot2 ( Ren %systemroot%\system32\catroot2 *.bak )

  b. Reset the BITS service and the Windows Update service to the default security descriptor.
 Commands:

• sc.exe sdset bits D:(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA)(A;;CCLCSWLOCRRC;;;AU)(A;;CCLCSWRPWPDTLOCRRC;;;PU)
• sc.exe sdset wuauserv D:(A;;CCLCSWRPWPDTLOCRRC;;;SY)(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;BA)(A;;CCLCSWLOCRRC;;;AU)(A;;CCLCSWRPWPDTLOCRRC;;;PU)

3. Reregister the BITS files and the Windows Update files.
Commands:
cd /d %windir%\system32

• regsvr32.exe atl.dll
• regsvr32.exe urlmon.dll
• regsvr32.exe mshtml.dll
• regsvr32.exe shdocvw.dll
• regsvr32.exe browseui.dll
• regsvr32.exe jscript.dll
• regsvr32.exe vbscript.dll
• regsvr32.exe scrrun.dll
• regsvr32.exe msxml.dll
• regsvr32.exe msxml3.dll
• regsvr32.exe msxml6.dll
• regsvr32.exe actxprxy.dll
• regsvr32.exe softpub.dll
• regsvr32.exe wintrust.dll
• regsvr32.exe dssenh.dll
• regsvr32.exe rsaenh.dll
• regsvr32.exe gpkcsp.dll
• regsvr32.exe sccbase.dll
• regsvr32.exe slbcsp.dll
• regsvr32.exe cryptdlg.dll
• regsvr32.exe oleaut32.dll
• regsvr32.exe ole32.dll
• regsvr32.exe shell32.dll
• regsvr32.exe initpki.dll
• regsvr32.exe wuapi.dll
• regsvr32.exe wuaueng.dll
• regsvr32.exe wuaueng1.dll
• regsvr32.exe wucltui.dll
• regsvr32.exe wups.dll
• regsvr32.exe wups2.dll
• regsvr32.exe wuweb.dll
• regsvr32.exe qmgr.dll
• regsvr32.exe qmgrprxy.dll
• regsvr32.exe wucltux.dll
• regsvr32.exe muweb.dll
• regsvr32.exe wuwebv.dll

4. Reset Winsock.
command: netsh reset winsock
5. Restart the BITS service and the Windows Update service

• net start bits
• net start wuauserv

6. clear the BITS queue
command:
bitsadmin.exe /reset /allusers
7. Restart the computer
**************************************************************