PC Reboots

I have a workstation running W2K Pro. Everytime a user tries to open a document in Adobe Acrobat Reader 5.1 and zoom in or goes to a web page with Flash graphics with IE6, the PC reboots. There is no error displayed and there is no BSoD. Memory usage is good. I have applied all critical updates and service packs. I have tried a different video card, but that didn’t solve the problem.

If anyone can help out, that would be awesome.