W2K-prof hangs on restart or shutdown??

I need some help, my win2k-prof box hangs with a blue screen when I try to shutdown.
All the hardware is check and is OK. I have to press the on/off or reset-swithces if i need to work with it again. Any help will be appreciated. I did install SP1.(maybe the new ATI-drivers form their website–do anybody had the same experience). Thank you.