Ok, any time i try to play a game it crashes. For example: Battle for middle earth, Flyff(Fly for fun), Etc. It starts fine but when the actual gameplay starts it starts like messing up, like if it's glitching. Please i need help with this thank you.

Is it a new problem? Did these games play OK previously?

They used too. But when i re-installed windows xp, they started messing up

Did you reinstall the graphics drivers?

Yes, i re-installed everything it had before.

Actually this has been happening for some time just haven't been playing alot.
But, it happened right after the window installation.

Have you opened the case and checked the fans as well as general cleaning?

You symptoms are very indicative of over-heating.

Well, how would i know if it's overheating? And yes i do Clean my pc. All my fans are working, but this computer is custom built so it might be a problem with overheating.

It's not that long after it starts that it crashes. Probably, like 20 seconds after it starts.

If your only problems are running full screen games then I would suspect heat or an inadequate power supply.

How to know? All I can suggest is trial and error. I would run with an open case and even blow a room fan on the board. See if that changes anything.

You can also get a PSU tester for the power supply but again if the issue is only with full screen games I would suspect your graphics card.

Do you have another card you can try?

Is it freezing? Or does Windows continue to work? If the latter:

Check your Event Viewer via Administrative Tools.

Open the System as well as Application tabs and look for red X errors that coincide with your problem. Details here:

http://support.microsoft.com/kb/308427