I have been having some issues with my PC since I installed my new Gigabyte GTX660 OC graphics card where the system will randomly reboot. When the system does reboot though, it's like power is cut from the system where no motherboard lights or case LED's remain on. I have performed extensive tests to rule out potential causes, but I am now at a loss short of replacing the motherboard and CPU prematurely. Prior to this card, I had an ATI HD5870 and my system was randomly locking up. I believe this was caused by 2 x 1 GB ram sticks I have since removed, discovered through this testing phase and I have not observed lock ups since, just reboots which have only existed since installing the GTX660. Reverting to the ATI card has proven reboots are isolated to the GTX660.
Strangely, when I play a game, I can play for hours with no reboots. However, in Windows doing anything simple will sometimes cause a reboot. This isn't days between reboots, it can be from a minute after booting into Windows, to an hour to all night reboot free if the computer is left unattended and unused.
Gigabyte GA-P55A-UD7 motherboard with latest BIOS flashed
Intel i7-870 CPU not overclocked
4GB g.skill RAM
OCZ Vertex 3 120gb SSD
500gb Western Digital 7500rpm HDD
Corsair VX550W PSU
Running Windows 8 64bit from the SSD.
PSU tests: Initially, I thought it was the PSU. I performed voltage checks on all connectors from the PSU with 3.3V, 5V and 12V all within tolerance and not far off perfect. I put a watt meter inline to the PSU from the wall and Max power draw is no more than 53W at idle. I haven't tested under load as playing a game with highest video specs has been fine.
Heat: System is dust free and coretemp shows under no load that I am averaging about 40 degrees celcius across 4 cores. Under load it'll get to about 58 - 65 degrees. I moved the card away from the first PCI-E slot to the alternate PCI-E 16x port which has had improved thermal results being further from the main motherboard components. Cooling in the house and good air flow through the case exists so I'm confident heat isn't the issue.
RAM: I've performed memtest with no errors being observed. Reseated them, changed RAM out completely with brother in laws RAM as a replacement: it's not the RAM.
Hardware isolation: Removing the 2 x non g.skill ram sticks seems to have resolved my random lock up issue, however reboots still exist. During this phase I removed power from non-essential hardware like the DVD-ROM drive, but reboots still occurred. The motherboard appears to be in good working order with all the capacitors looking healthy. Running latest bios for motherboard and no vBios exists for my GFX card to update.
Drivers: I have tried running the drivers from the CD that came with my GFX card; no go. Drivers from the website, drivers from the gigabyte website. I even reinstalled Windows 8 using the Win 8 Refresh tool and same thing happening installing only the drivers after the Win 8 refresh to rule out installed software being the cause. I am steering towards this being a driver related issue, but surely others would be seeing the same thing and google flooded with complaints and fixes? I have used the included drivers, recommended drivers and latest drivers to no avail. *Note: When using the standard generic gfx driver with the nVidia ones uninstalled, I cannot replicate or force the system to reboot. The same happens in safe mode where the system hasn't rebooted itself. Once I install the drivers is when the fun begins and my hair gets pulled.
Windows 8 event log only shows system powered off incorrectly and nothing else of use. I've run a few diagnostic tools and my hardware appears to be healthy. Hard drives are showing to be healthy also after running disk checks.
Like I said, I am at my end to what else I can do short of replacing the motherboard and CPU.
Any assistance would be greatly appreciated. I am an 8 yr Electronics technician by trade and this has me absolutely stumped.