Windows NT logon problem

I was asked this problem by a colleague and honestly didn’t know the answer. I hope you can help! On a Windows NT 4.0 Workstation, the initial CTRL+ALT+DEL key combination that is required at logon is not responding.
Whenever the key combination is pressed, nothing happens at all! Using the last known good configuration profile option had no effect. Keyboards have been switched with known good ones and it still doesn’t allow acess to the logon screen. Can someone please help with this dilemna?