Games Crash after a few mins of play.Follow

Hi all.

I have just today bought a new PC, as my old one had completely gone wrong, and fixxing it wasn't worth the effort.

Anyway.. to the problem. I have not yet installed World of Warcraft, however, the games that I do currently have, Ragnarok Online and Warcraft III, are both suffereing from this problem.
I'll start with Ragnarok. I was looking forward to getting a new Pc, as I have recently bought a wireless router, and thus was hoping that me and my bro would be able to play the game togther. Ok, so all going well for a few minutes when bam, he shouts me and tells me the computer has just rebooted. We try again, and the same problem occurs.

So, onto Warcraft III, I start playing, and set up a local area network game. So a few minutes into setting it up, and my bro shouts me again, and to my shock, the computer has crashed (not rebooted, just froze) and only a manual restart could get things back to normal.
So we decide to start again, and upon trying Warcraft III again, after a few minutes, as what happned with Ragnarok, Warcraft III rebooted also.

These are the specs to the compter with the problem:

2.8 GHz Intel Pentium D
256MB nVidia GeForce 6200 LE Graphics Card
1024 DDR RAM

If anyone knows a fix to this, please, I would be most grateful.
If the graphics drivers do need upgrading, could any of you possibly tell me which downloads to take off the nVidia site, as there a alot there.

Thanks in advance.

i dont know if this is the same but my FF11 is crashing to. ill log on and i can play from eather like 30 seconds to 3 hours and if im on windower it gives me an error report and if im on full screen mode the screen just goes black and goes back to my desktop. im computer retarded if u read my other posts so i have like really no clue what im supposed to do.