PC shuts off in the middle of some games!

I Just upgraded my processor from a P4 2.66Ghz to a Core 2 Duo E7200 2.53Ghz. I had to buy a new power supply too because the first one would make loud noises whenever 3D games were running. The PC works fine now most of the time, except that on certain games, and in 3Dmark2003 (at a certain part of the Nature Test), the PC just shuts off! As if someone pulled the plug!

Can anyone help me narrow down the cause of this? the only thing i changed was the processor, and the power supply. I don't know what problem causes this kind of behavior. The games that cause the PC to shut off by itself are Mass Effect, Oblivion, and World In Conflict. But i can play Gears of War, and Command and Conquer 3, and Race Driver Grid for hours without the PC shutting off.

BTW, in Mass Effect and Oblivion, i can usually tell when it's about to shut off, because i start to hear a faint stuttering sound coming out of the speakers. Kind of like static but it's stuttering.

My specs:
Core 2 Duo E7200 2.53Ghz
Geforce 8600GT 512mb DDR2
ECS 945GCT-M2 / 1333
1GB DDR2 ram at 667MHz (i think it's 667)
500W Power supply
1 DVD-Rom drive, 1 CD-Drive, one Hard disk. That's it.

RAM may be a problem..also whats your OS??

I have SpeedFan, the CPU and both cores barely go above 55deg even during games. The 8600GT has a ceiling of about 70deg on some occassions but it's rarely gone higher than that. And the games crash within 15 minutes of playing, whereas Race Driver Grid and Gears of War can be running for hours with no problems. I'm really curious about the stuttering sound coming from the speakers. In Oblivion for instance, the stuttering gets louder when i'm facing a lot of trees or buildings, and lessens when i'm facing straight down at my feet where there's less geometry.

I don't know if this info helps, but i discovered that if i run 3Dmark2003 Nature Test at 640x480 or 800x600, the pc doesn't shut off. Once i bring it up to 1024x768, it's a 99% chance it will shut off at the exact same point. Does this narrow down the cause in any way? From what i understand, the stress on the CPU doesn't change if you switch resolutions, only the video card gets stressed, is that true?

Since the only other thing you changed is your psu, that just might have something to do with it. Seems unlikely though since some games apparently give no problems at all and I would expect you to have other problems to go along with shutting off. Still, is it a reputable brand? Do you still have your old psu to see if the problem stays the same while using that?

But first I would look into what Aldouz said about possible compatibility problems. It is an older chipset afterall and it doesn't seem unlikely that that could have some influence on your on-board sound (which I assume you are using). Did you update to the latest bios version?

Looks like tour CPu is overheating under the load.Try CPU-Z and see how much the temp is.

Make sure that the fan in working properly.Try to increase its speed and then see.

Try a thermal paste like artic silver for the CPU.

This is all the info printed around the box of my PSU:

iMaster Pro 5000

100V-260V selectable input voltage

120mm Cooling Fan

8cm Exhaust Fan

4 x Sata

20+4 pin DC connector

3 Big + 1 Small

Cord Shield

Electroplated

According to Speedfan, here's all my voltage stuff (sorry i'm not really a techie overclocker person, i'll just type what i see):

Vcore1: 1.04V
Vcore2: 1.82V
+3.3V: 2.03V
+5V: 5.08V
+12V: 8.13V
-12V: -12.61V
-5V: -5.31V
+5V: 4.97V
Vbat: 3.38V

I have no idea what those are but i sure hope they're bad numbers (coz i wouldn't want anything else to be broken but the PSU).
By the way, do those numbers change when gaming? because i got those numbers when the system was idle.

According to Speedfan, here's all my voltage stuff (sorry i'm not really a techie overclocker person, i'll just type what i see):

Vcore1: 1.04V
Vcore2: 1.82V
+3.3V: 2.03V
+5V: 5.08V
+12V: 8.13V
-12V: -12.61V
-5V: -5.31V
+5V: 4.97V
Vbat: 3.38V

I have no idea what those are but i sure hope they're bad numbers (coz i wouldn't want anything else to be broken but the PSU).
By the way, do those numbers change when gaming? because i got those numbers when the system was idle.

onch

The difference should not far... well I'm not expert with PSU..

maybe you can as RayvinAzn, he know much about this...