Problem - Possible RAM or GPU Issue

Hi everyone, first of all, I'm Nathan, and this is my system:

Gigabyte GA-EX58-UD4P
Intel Core i7 920 2.66GHz, not overclocked (except for the standard dynamic overclocking)
Gigabyte nVidia GTS250 Overclocked - Part # GV-N250OC-1GI
Corsair TR3X6G1600C9 6GB DDR3 1600MHz
720W Gigabyte ODIN PSU
Windows Vista Home Premium 64-bit

Now I've had problem on problem since I built the system. I myself am a computer technician and haven't been able to fix this issue, and reluctantly, am asking for help as I'm truly stumped. The issues (and what I've tried to remedy them) are: (P.S I'm pretty sure all the issues are related)

If left idle for more than roughly 20 minutes, it will just reboot. Not even a blue screen of death. I know for certain there's no blue screen as I've turned off the automatic restarting in the event of a memory dump.
I've tried turning off all power saving features on any and every component I could find, this didn't help.

Normal activity usually does NOT attract any blue screen or reboot of any kind. Even watching movies for hours without any input prevents this. However the last few nights it's been blue screening with a "PAGE_FAULT_IN_NONPAGED_AREA" STOP 50 error. There are many conflicting views on whether this is hardware or software related; lots of people pointing at both graphics and RAM. I currently have my memory clocked down to 1066MHz as this was one of the methods I tried to remedy the situation, however it didn't seem to help.

If I go into device manager and open the properties of the nVidia card, and then under the drivers tab click the "Driver Details" button, it hard reboots, no blue screen. I installed the latest driver from the nVidia site. This did nothing. I rolled back to the driver that came with the card, no luck. Tonight I've just installed the newest driver from the Gigabyte website rather than nVidia, and alas, I can open the driver details from device manager without a reboot. I then went back into my BIOS and changed the RAM to it's specified speed, 1600MHz, by using the Intel XMP Profile 1. Once booted back into windows I again opened the driver details of the graphics card, only to find it rebooting. Now back onto 1066MHz again, open it up, and it works no problem.

I've tried booting into safe mode to see if it will idle without rebooting, to determine if it's a driver issue or hardware issue, however when trying to boot safe mode, it pauses at crcdisk.sys before attempting to load the logon screen. All I can see is the cursor for maybe 2 seconds, before it reboots.

Additional things that I have tried/looked at already:
CPU Temperature - has never risen above 45 degrees celcius.
RAM - This is definitely 1600MHz rated RAM, compatible with my board and chipset. Confirmed by http://www.corsair.com/_datasheets/TR3X6G1600C9.pdf
Event Viewer - The only information that is provided by the logs in this is that the previous system shutdown was unexpected. None of the other events prior to this correspond to anything. Usually there is a gap before the shutdown. E.g. Previous system shutdown at 10:15:22 was unexpected. The last activity before this time may be 10:01:41.

Has anyone got any idea why this could be happening?

 

Run MemTest over night to check if it's RAM related
http://majorgeeks.com/MemTest_d350.html
Also re-sit your graphics card and & RAM and have you installed any drivers or anything lately?

 

I ran Prime95 last night with a standard balanced stress test, it blue screened in 15 seconds flat. I had ran memtest86 a fair while back to check if this was the issue, yet it found no errors in the RAM, yet it couldn't complete the CPU tests.

 

Okay so you have an i7 and therefore no FSB? Previously RAM MHz was significantly correlated with FSB MHz and a ratio had to be achieved for them to work in sync. I believe one of the current restrictions with the i7 is that RAM MHz (i.e freq and not timings) will have a significant impact on the CPU throttling and can cause it to OC and or not work. The primary cause of this I believe is the over voltages being delivered to the CPU (which are now a lot lower) due to the RAM. Look into the voltages, slow your RAM down even further because from what I read 6 months ago the RAM can and will have a detrimental affect/impact upon the CPU. Sorry but the I7 has introduced a whole new way of thinking about the problem......

 

One thing has sprung to mind. When you boot up next go into your RAM BIOS settings and take note of what the values for vDIMM are etc. If you have the settings to SPD (therefore auto) sometimes the BIOS can be setting your Voltages a little bit higher when you get into the OS. The specs indicate that vDIMM should be at 1.65v and timings at 9-9-9-24 sometimes the BIOS SPD settings can make ths differ from manufacturer specs. Firstly I would run CPU-z while in OS and see what the current values are and then I would consider manually setting all ths values within BIOS to note if that improves things.