I posted this as a reply to another post, but I figured I would make a new thread just in case it may be usefull to people who are having this issue. I modified it a bit to be generalized, please feel free to add comments/revisions to help those who may be in need of a resolution:
For anyone who may have a problem with their computer locking up or 'freezing':
This may be faulty memory. Try running a memory test program, or trying new memory to see if that is the issue.
If your memory is fine, or if new memory works fine, then run a full scandisk (fdisk) on the hard drive to see if there are bad sectors.
Try another video card, if you have a cheap old reliable one laying around, to see if video is the issue.
If all three are fine, reinstall the OS - assuming you are running Windows, and that you have already troubleshooted the OS itself withour resolution (i.e. Driver updates, OS updates, etc etc.). If Linux, then run the appropriate hardware tests and software tests and you should not have to reinstall the OS.
If you go through all the above steps and the issue is still prevelant, try a new motherboard or power supply. But do those lastly, as most likely the problem (and cheapest to resolve) is the memory.
Make sure you have the appropriate power supply. Take note, the cheaper the motherboard, sometimes equals to power consumption issues which require higher-than-normal standard power supplies.