Intermittent No login prompt on Window 2003 Server

[icetrap]

No Login Prompt, no response on the mouse.
Keyboard "caps lock" working.
After depress "Ctrl + Alt + Delete" , Server did not response with a login prompt.

-Server is behind a KVM switch but that it not the issue as the KVM was reset and tested = still same issue.
-Rest of Server connected with the KVM is working fine.
-Swapped KVM port with another server = result same issue.

-Problem was only resolve by cold reboot of server.

I am suspected some services is causing the issue or could it be due to the active directory issue?