Have you tried running the games in XP sp3 mode?
Most of the games I've played are recent games, developed primarily with Vista and Win7 in mind, so this shouldn't be necessary. I haven't tried it.
Is this pc still under warranty?
If it is bring it back and tell them the issues you are having since you bought the machine.
Kind of a long story. Because they built it, I have a one year warranty. I took it back about a month after getting it. They couldn't duplicate it, but I think you really have to play games to make it happen. Artificial tests like Prime95, Intel Burn Test, etc don't seem to trigger it. Since it's random, who knows for sure though, could just be fluke or not on long enough. And of course, they aren't playing games like normal. It seems they try to trigger the problem with stress tests and/or leaving the game on but not actually playing.
Anyways, I ended up taking it home and hoped I could figure it out myself but that got me no where. Recently I took it back again. They agreed to switch the PSU temporarily with one they had in the back. I took the machine home but different PSU was no help.
Now they will RMA the mobo for me and put in a new one once they get it on hand. Unfortunately, they don't want to let me get a different make/model and to be honest I have no confidence in this Asus product. Chances are it's a problematic board, based on a lot of Googling. But I'll see how this goes once they put it in.
Have you run memtest86+ on each stick of ram to see if the ram is tossing errors?
I ran memtest overnight and it passed, but not the one on bootup so not all the ram was tested. But the shop said they tested it and it was OK.
Did you run the hard drives diagnostic on the hard drive? You can get it from the hard drives web site.
No, but I ran the windows scandisk which came back OK. Since CPU downclock is the only thing that's worked, and with the PSU ruled out, it's got to be the mobo or the CPU itself.