1. Server online – Check if server is powered on.
2. Server accessible - Check if server is online in network.
3. Check Network - Check if network cables are plugged in. Check TCP/IP settings and change if necessary.
4. All services running - Use services MMC to check if all services are running.
5. Logon using RDP - Logon as a user to check if it is a Citrix problem or not.
6. Logon on Console - Logon as a normal user on the console.
7. Administrative logon - Logon as a administrator on the console

8. Debug logon process - Set the following registry key on the server to debug the logon process:
Key: HKLM\Software\Microsoft\Windows NT\CurrentVersion\Winlogon
Value: UserEnvDebugLevel
Type: REG_DWORD
Data: 10002 (Hex)
The data value of 10002 will enable verbose logging to a file on the server. Once you set this value, reboot your server and check for a “userenv.log” file in the %System Root%\Debug\UserMode\ folder. Remember to turn this off when you’re done troubleshooting it, since each user logon can easily add 100KB to the size of this log file.

9. Member of domain - Check if the server is still a member of the domain and if the server can successfully contact the domain controllers.
10. Start Services - Start the services which are not started
11. Citrix Related Service - Is the failing service a Citrix Related Service such as the Citrix XTE server or the Independent Management Architecture
12. Check Event Log - Check the Event Log for warning or error messages. Lookup the Event ID’s to check if it’s a known error.
13. Fix error - If the error message is a known error fix it according the given resolution.