Computer Crashing While Playing Tomb Raider Anniversary

[darbanator]

I just finished reading the post concerning ATI card problems of overheating while playing games. I have an ATI Radeon X850 Pro AGP card and am having similar problems. I've taken my computer to local Computer Repair facilities only to find the problem was not corrected. All that happened was my dishing out $100+ to have it cleaned. What's happening is after about 10 minutes of gaming, everything locks up and I have to soft boot my computer. I followed the instructions for downloading ATI Tools but am a little squeemish about installing and properly using it to change the fan speed. I'd take the computer back in again but I just have a problem paying that much for another cleaning. All my system hardware exceeds the games minimum requirements. I have two fans for cooling and just can't understand what needs to be done to allow me the pleasure of uninterupted gaming. I really need help from someone who knows a resolution and can relate to a novice user. The following is the specs of my system (as far as I know):

Processor: Intel Pentium4 3.06 GHZ
Motherboard : ASUS P4S800D-X
Ram: 1 Gig
Display Adaptor: Radeon X850 Pro 250MB
O/S : Windows XP Pro SP2
Soundcard: Audigy

As I am what would be considered a Novice, I appologize for any information I did not include. However, I would be more than willing to at least attempt to locate any further necessary information as needed to help diagnose and cure this frustrating problem.

Thanks to anyone who takes the time to read and hopefully assist me.

[Getout2280]

You can alway open the side of the case and have a box fan blow directly onto the computer. If you do not crash like normal it is probably a heat issue.

[XDE]

Does it crash or it automatically restarts the PC ?

[darbanator]

It just locks up ... followed by a series of clicks. The only way I can get it to reboot is by pressing the soft boot button.