[link|http://64.233.187.104/search?q=cache:Zu3Geh2lm3IJ:www.experts-exchange.com/Operating_Systems/Q_21568625.html+CLASSPNP.SYS+crash&hl=en&client=firefox-a|Google cache]. Scroll down.
Bad RAM? Overheating? Is your power supply fan running?
If I had to diagnose the hardware I'd start with the power supply and work from there. Have a Knoppix or MEPIS or similar bootable/installable Linux CD handy if you can. (Ubuntu comes in 2 versions - bootable and installable.).
HTH. Best of luck!
Cheers,
Scott.