It is probably not your video card. What brand and model is your motherboard? You likely have bad CPU capacitors (almost 100% probability, from your description).

k7s6a by Mainboard

whats your power supply rating and manufacturer? Also good be your memory, software memory testers may not catch all errors, but they catch most. Here's a decent (very decent for free) one:
http://www.majorgeeks.com/download.php?det=3955
and if you want to check the CPU on your machine, try this: http://www.majorgeeks.com/download.php?det=273

Reason why I ask about your power supply is that a under rated power supply can cause lock-ups too. Just some back ground on the machine:
Is this a recent problem on the machine?
If yes has anything been added (software or hardware) to the machine?
If no, how long has this been occuring, and can you think of anything, anything at all, that might be related to this behavior?
If you think it's your video card, really simple way to fine out is go by a tech shop, ask one of the tech guys if they have an old, piece of crap PCI graphics card they want to sell (don't pay more than $10 for an old Trident 4MB PCI). Uninstall your graphics card (drivers and all in device manager), install the crap one, and see if you experience the same problems.
You can try moving to a different power outlet. Sounds silly, but can cause problems. Also, you can get what they call a line conditioner for your power (basically a really nice power strip. Same think UPS's use without the battery part. Cost about $25. If you buy it from Wal-Mart, and it doesnt work, you can take it back and get your money back, tax included) It basically smooths the power out to your machine if the outlet you are using is causing sporadic power spikes/dips. Etc... let me know

While the ECS K7s6a is not known for having this problem, it's easy to check visually. See the picture below; the nine components circled in white are the CPU capacitors (caps) -- six to the left of the CPU socket in the photo, three below and to the left of the first group. This is one case where a bad part is visibly defective -- a bad cap will either have a bulged or split top or be partially lifted off the printed circuit board. There may be a black or brown goo leaking out the bottom(s) of the cap(s) as well.

Sardukar is at least partly right -- the problem could also be the power supply. Check to make sure that the exhaust fan is spinning properly and not clogged with dust. If the fan is spinning slowly (or not at all) the power supply will run hot, eventually bake. The caps will dry out, and the voltage will vary, causing lockups.

Memory tester:MemTest86.

Sardukar is at least partly right>

G, thanks? :rolleyes:

I did not mean to insult or denigrate. I've been an electronic technician for over forty years and wanted to be as clear as possible -- and remember, I said at least partly right. I have done component-level repairs on power supplies and motherboards for over 20 years, so I have the background to speak to this.

I apologize if I offended.

I had nasty locking up problems. Fixed it by defragmenting my hard drives.