I've tried everything I can possibly think of in trying to fix this problem and I'm totally out of ideas, so any help would be appreciated:

The problem: whenever I fire up a game, it works for a short while with no problems and then it would crash. Either its a hard crash, forcing me to reboot, or windows would report that the display driver has stopped working and recovered. Here is a list of things I've already tried:

1. Drivers - tried the latest drivers (catalyst 9.12) as well as the stock drivers that came with the video card. Also have the latest BIOS/chipset
2. Memtest - Ran Memtest86+ overnight, had no problems, the windows diagnostic tool also does not find any problems.
3. Overheating - Video card/cpu temperatures are well below peak (42 and 31 Celsius receptively)
4. PSU Voltage - CPUID shows that the voltage levels are all above what they should be. The PSU itself is only roughly 16 months old and is a good model.
5. HDD - No errors when checked
6. GPU - Brand new (replaced previous card since I thought it was the problem, apparently not)
7. Overclocking - Everything is at stock levels, memory voltage is set to manufacturer's standard

Specs:

• Motherboard: ASUS P5Q Pro
• CPU: Core 2 Duo E8400 3.0 ghz
• OS: Windows 7 home premium 64 bit
• Memory: Mushkin Enhanced 4GB DDR2
• GPU: Sapphire HD 5850 1GB
• PSU: SeaSonic M12 600W ATX12V
• DirectX: DX11

Event Viewer after a crash always has these logged:

A fatal hardware error has occurred.

Reported by component: Processor Core Error Source: Machine Check Exception Error Type: Bus/Interconnect Error Processor ID: 1

The details view of this entry contains further information.

A fatal hardware error has occurred.

Reported by component: Processor Core Error Source: Machine Check Exception Error Type: Bus/Interconnect Error Processor ID: 0

The details view of this entry contains further information.

A previous card that I had (4850x2) also had these errors, so I changed video cards, but the same thing is happening.