This is a good place to start. http://support.microsoft.com/kb/814546
This page gives instructions on using dxdiag, ect.
I would suggest checking the wattage on the PSU, check to see if your Vcard has an extra power plug, if so, you need to plug it in. Low power could damage your system, and your HD shouldn't shut down. You may need to flash your BIOS, run a checkdisk on your HDs, check off the boxes for checkdisk, (disk properties, tools menu) defrag the HD after your finished, and you can check on you system hardware, here's an example:
HereJust incase, you need to make sure all your updates for microsoft are up to date, and get spysweeper, or something similar, there are some nasty rootkits everywhere. Also, turn on DEP for the system and all programs, example:
HereThere are alot of resources on the net, microsoft has alot of diagnostic tools, like MBSA. and more.
Here