I just reformatted my PC and reinstalled windows vista..
Whenever I try to play games after a while my PC freezes.. =___=
My PC uses GeForce7300 SE and has a memory of 509 MB..

The same thing happened the last time I formatted it.. Although I don't know what I did to make it stop hanging.. And now it's back T_T What should I do...? Thanks ^___^

One of the most common causes especially with games (which stress the system more than anything else) is overheating. Clean out the case of dust, especially check the CPU heatsink for buildup inside the fins under the fan. Check all fans are spinning up to speed. This includes dust in the power supply. A quick test is to open the case and put a window box fan blowing in; if your freezing stops you have your answer-overheating. If no joy, run Memtest on your memory - see the hardware section, pinned post "Homebuilding Techniques" for more info on Memtest.

I think you haven't installed your video card driver that comes together with it.
try the following:
1. install your motherboard drivers for all chipsets and controllers then reboot.
2. install driver for video card then reboot.

I hope this fix your problem