Alright.. for memtest instructions follow the link in my signature. Use another PC to burn the bootable CD or create the floppy if you have trouble with doing it on your's
Navigate to the C:\Windows\Minidump folder and post 5 of the most recent ones here as attachments.
Go back to msconfig and in the first page you're presented in, choose Diagnostic Startup. Reboot and see whether your pc is much more stable now. Nero won't work in safe mode because some of its components are not loaded. Diagnostic mode should do the trick for nero, but if it doesn't, go to the Services or startup tabs and tick any entries relating to Nero or Ahead.
To open your PC simply unplug it from the wall outlet and go to the back of the tower. You should see four or six screws on the edges of the back, holding the side cover in place, and the 2 on the right side should let you have access to your insides once you slide it off. If its a one piece cover, then undo all of the edge screws and all you need to do is simply slide the case off.
http://www.helpwithpcs.com/upgrading...ase-covers.htm
While you have your PC opened, take this opportunity to clean it out of any dust buildup with a compressed air source and inspect for any sort of damage like burns and capacitor damage..