When temperatures outside are high (80+ degrees fahrenheit), and I'm playing a game as well as having firefox and other things open (basically high loads), my computer will sometimes freeze up and POWER to all of my peripherals goes out, but the computer doesn't actually shut off until I hit the button.

I regularly monitor my CPU and GPU temperatures, and my CPU hovers between 35-45 degrees celsius while my GPU hovers between 45-55 degrees celsius. SOMEONE mentioned to me that it could be memory failure, so I ran a memtest, but it didn't come up with any errors through 1 and a half passes.

I also just replaced my PSU which was my oldest piece of hardware so that can't possibly be the issue since it was happening before I replaced it.

Any ideas on what could be causing my freezes would be greatly appreciated.Next step would be a hard drive diagnostic test and posting your computer specs. or model. From the numbers you posted regarding temps. in F, there is not an indication of heating problem since those hardware are still unknown.My current hardware:
CPU: i5 2500K 3.3 GHz, ~3.6GHz
GPU: NVIDIA Geforce GTX 560ti
Mobo: Gigabyte Z68X-UD3H-B3
RAM: 8 GB Ripjaws DDR3
HDD: 1 TB WD Caviar Black
Windoes 7 64-bit Home edition

Is there any program you recommend for hard drive test? I ran a test with the one provided on WD's website and it says there are no issues, but I'm not sure how RELIABLE that is.