|"Im guessing the video card just because i have had trouble with it before."|
Like what kind of trouble?
I suggest you get the power supply replaced before you sell it (the computer is probably not even worth that much anyway). EMachines are built with very cheap power supplies from a manufacturer called Bestec. Bestec makes about the worst power supplies around. They are made up of cheap capacitors and parts. I suggest that you get the power supply replaced ASAP because if it blows, it usually blows out the motherboard with it. Even if the power supply isn't the culprit for the freeze-ups, get it replaced anyway because it still could blow at anytime.
Replace with a micro-atx power supply with a maximum load of 350W at the minimum.
After you get that replaced and you find that it still freezes, boot it up into the BIOS and let it sit there for awhile. Does it freeze? If so, run Memtest86+ on the system for 12-24 hours.