hello when I play gears of war or any other demanding games my pc will reboot within a few minutes of playing

my cpu cores @ idle are ranging from 28-36c
and when gaming 39-45c in coretemp! so i don't think its my cpu!

my p5ne-sli temp according to Everest Ultimate
at idle is 33c and gaming 36c so this is not bad right? and my 8800gtx is @ 54c idle
and 58-59c gaming witch is normal right!

I have no temp monitor for my (Crucial Ballistix Tracer 4GB DDR2 PC2-6400 with LEDs) but they are cool to the touch.

I have a high quality Corsair HX620W psu
and the air that comes out of it is warm
normal right!

and I just formated to see if it would be software related but I just played and it happend to me again?.....might it be cause I Have 4gb of ram? as i can remeber everything was fine when I had 2 gigs the latency is at 4-4-4-12 stable! and i memtested them for 3 hours with no errors
so if you guys have any ideas pls help I'm a gamer lol

Win XP is set by default to automatically reboot when it encounters an unrecoverable error.

To have XP possibly display an error message you can investigate instead of the computer rebooting:

1. Click Start, and then right-click My Computer.
2. Click Properties.
3. Click the Advanced tab, and then click Settings under Startup and Recovery.
4. Under System failure, click on the small box beside Automatically restart to remove the checkmark.
5. Click OK, and then click OK.

If you then get an error message, look at all of it's details.
....

If that yields nothing........

Sometimes a PS can become defective such that it will do flakey things like you're experiencing when you are putting more demands on your system.
E.g. My brother had an Antec that worked fine for over a year, then it would reboot when more load was put on the system.

Failing power supplies are common and can cause your symptoms.
Check your PS.
See response 4 in this:
http://www.computing.net/hardware/w...

If you find no obvious sign of something wrong with it, as I did with my brother's Antec, try another PS anyway. Don't buy one if you can borrow one to test with. Doing that confirmed it was his PS and not anything else - it was probably the chip that controls the PS that malfunctioned - it controls how the PS responds to the load placed on it, amongst other things.

If both your CPU & RAM are running at their default frequencies (CPU @ 266MHz, RAM @ 400MHz), manually configure your RAM to run at 266MHz (DDR533) to match the CPU.

If that doesn't help, try temporarily running with just 2 sticks of RAM. If it's OK with 2 sticks, try 3.

Don't be concerned about dual channel mode for now...you're troubleshooting.