NT Shutting down problem

I have a couple of customers that are having a strange problem with Windows NT SP5.

When they try to shut down their PC, the PC screen shades and then does nothing. It will sit there until you press CTRL+ALT+DEL. You can then shut it down without any problems.
They don't have roaming profiles and they don't get any error messages. If you press CTRL+ALT+DEL, it takes you to a log on screen, not task manager. I have checked event viewer and there is nothing listed there.
I am not sure what else to check and I don't have any idea what can be causing this. I looked on TechNet and I couldn't find anything specific to this problem.
Any ideas would be appreciated.
Thanks,
Dave

Does it shutdown eventually (10 -20 Minutes) or does it lock solid?Try to shutdown at command prompt with
shutdown /C /L /T0
Try reinstalling the service packs again.
Good luck

NT will just sit there. I am not even sure you can say it locks up. I can move the mouse and Press CTRL+ALT+DEL.
I will look at reinstalling the Service Packs.
Thanks,
Dave

For those that are interested. We resolved this problem yesterday afternoon. It looks like it was the Office toolbar. Both users had the toolbar minimized instead of sitting on top of the screen or on the side. Once we moved it to the side. The PC started to shut down without any problems.
I guess you learn something new everyday.
Dave

Oh I hate that office toolbar. I usually disable it on any machine that I'm working on. It just causes problems.