computers: its a love/hate relationship

First off Im new here so hello major geeks and Im hoping you can help me with my problem. This being my first post I promise wont dissapear off the forum forever if you help me

Heres my problem:
My computer is not overclocked, i just figured that this issue would best suit this forum. If there is a tech support forum then I missed it and I blame it on my newbiness.

-Im running windows xp service pack 2 right now.
- AMD athlon 64 x2 dual core 6000+
- 4g ram
- Nvidia Gforce 8800 gt
- Antec 450 watt pwr supply

I can start up any game just fine get to the menu yada yada but as soon as I want it to load the actual game to play, my computer crashes completely - either shutting off or freezing the screen in a horrible pink and cutting off the sound. The only option when it does this is to turn it off. Some times it will not turn back on right away, and other times I will have to unplug it and leave it for a bit before i can turn it back on.

Now I've always laughed at people who do things like unplugging their computers to try and fix things but this seriously is getting crazy and it is the only way I can get it to turn back on.

Ive naturally thought that something was over heating and found that ( through using core temp and gpu-z)

cpu idles at: 64c (both cores)
gpu idles at: 70c

So I freaked because i figure thats really high for a gpu to be idleing at and figured my gpu was crashing my computer so as to not overheat. it also made sense because when I tried to play games it would put it over the edge but just doing simple things such as browsing the internet wouldnt. So I downloaded rivatuner and found that my gpus fan speed was running at 25%, so I cranked it up to 100% and waited for the temperature to drop.

cpu idles at: 64c
gpu idles at: 57c

Now I thought this was a more normal temp and would fix my problem but apparently not. I have been able to play games for maybe a half hour at a time but they still crash and lately they wont let me play at all theyre doing the same thing they did before.

I got a tip from a guy at ncix to change the thermal compound on my cpu because it was a couple years old. I changed it and saw a huge improvement. At the moment my cpu is running at 39 c


Im looking for ideas guys where I should turn to next. By the way I know for a fact that all newer graphics intensive games crash my computer, but I have been using oblivion max settings to test if my ideas work. It always crashes right after the opening video to the game.

thanks in advance for your help guys, if you need any more info please ask and ill post it quickly

 

Well, power supply and temperatures are clearly not your problems. Any chance you have the computer overclocked? Have you updated your graphics driver to the latest version?
http://www.nvidia.com/object/winxp-266.58-whql-driver.html