PC Lock Ups

I know this is a tough thing to troubleshoot, but when running Windows NT 4.0 and you got a complete lock up on a PC and it happens fairly frequently, is it generally a lack of resources?

Now I’m not talking about the kind of lockup where you go to Task Manager and kill the app that is causing a problem, I’m talking about the kind of lockup where you can’t do anything. No mouse or keyboard functionality. So I can’t even check Task Manager to try to determine what is causing the problem. Theonly thing to do is power the PC off and then turn it back on.