When the Keyboard Fails
If the Server console keyboard fails, it is usually because the value for the keyboard buffer in the NT Registry is too low.
NT is supposed to be Fault Tolerant enough to weather this without bringing the system down.
The Good News: You may possibly still use the mouse. Inspect the Event Viewer and you can tell when the Keyboard Console process hung.
Do security work through the Backup Domain Controller and bring down the Server after hours and restart it.