When you login to Windows, all you have is a black screen. Task manager and other Windows shortcuts don't work.
To Resolve: Edit
1. Try to reboot into safe mode. See if you can login there.
2. If you can, try and determine if Windows is seeing a second monitor attached when there isn't one. Check your VGA cable connector.
3. Try to RDP to the workstation.
4. After checking graphics and monitor issues, see if it may be a virus.
If Desktop Comes After 5 Minutes:Edit
1. Check and see if you have any mapped drives that will not re-connect automatically. If you do, disconnect from them and reboot - should be fixed.