Here is my system:
Insulated Antec Solo Case
Abit IP 35 Pro Off Limits Motherboard
Core 2 Duo E6400
Arctic Freezer 7 Heat Sink Fan
Patriot 2x1gb PC5300 Dual Channel Kit
Zalman ZM600-HP 600W Power Supply
GeForce 8600GT XFX 256MB DDR3 DX10
Samsung LightScribe DVD-RW/CD-RW
2 x 750GB SATA Hard Disk Drives 7200 RPM
2 fans installed in front to cool drive bays
If the system failure is hardware related the cause could be anything from heat related such as overheating video card, bad sata cable to a dying monitor. It's hard to say, but basically there is a MB, CPU, RAM, video card, HD and PSU. Or course spare parts would be neded to troubleshoot the system hardware. If software related, perhaps a system driver is causing the system shutdown. Maybe consider updating the video card driver, MB drivers and other system drivers. Alsoinstall latest SP3 and all OS updates from MS. You could always do a repair install and bring the OS back to the point of the CD used to perform the repair installation of the OS. Beause you are loosing the picture, which video card driver are you using? The driver on VC CD is the one the card was tested to work properluy with. One other thing is to boot into safe mode and let it sit a while. If the system shuts down there it is likely hardware related.
So, in safe mode a lot of drivers are not installed that would be at desktop. Maybe one of the drivers that is not installed in Safe Mode is causing the system to crash. I suppose you could install/reinstall the video card driver and update Windows XP completely with SP3. You can always do a repair install of Windows XP if you have a install CD. This is assuming there is not a hardware problem causing the problem. I can give instructions to do a repair install if needed.