Hi
All I can suggest is that since it doesn't do it in Safe Mode then something you are loading is probably the problem.
You can try using "msconfig" from the run menu, to tell the computer to boot with minimal apps and see if you can track it down by adding a few at a time, i.e. if you add 3 and it starts having the problem then narrow it down from those etc.
Check to see if you can update things like your video drivers.
Mike