Do you have a sysadmin where you work? Or is this a home network?
You have to do a registry hack on your PC when using another computer, some programs and viruses change the logon program which causes this issue.
The key you need to change is
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\
It should be set to:
C:\WINDOWS\System32\userinit.exe