I own, an about a year old, rig which carries quite the punch. And for a year, I was happy. Not that long ago things began to crumble.

I first detected the problems running my dual monitor setup. For some reason, tearing and artifacts are appearing when I run with two monitors plugged in my nVidia GTX 460. I thought it was a graphics hardware problem and switch to an older RADEON 5850, but the problem did not go away.

I began experiencing BSODs on very specific things related to USB devices. If I shutdown the computer with my external banking security device plugged, it will BSOD, if I connect my external Rig Kontrol 3 audio interface it will BSOD as soon as I try to run any ASIO applications that use the audio interface. I also noticed magic ISO randomly blue screening the computer.

I've learned to avoid these BSODs because they are very predictable and the computer feels stable enough, but it also feels a lot slower than it used to be. The problem is that I have no way of actually measuring this, it's only a feeling I have, that something is a miss. If only there was to a way to compare my benchmarks against other systems with similar hardware.

This seems to be mostly noticeable during software installation processes and during draw calls in Windows.

I'm not ruling out that there's a problem with my GTX 460 card, but I think my motherboard is bad and thinking about replacing it. I've ran all diagnostic tools I know of (memtest, scan disk) to rule out memory issues and corrupt drivers. I've tried reinstalling everything, but to no avail. If anyone have any experience dealing with this kind of situation I love to hear about it. Because I hate to throw away money on something which wont fix the problem.

Edit

The motherboard in question is a Gigabyte P55 UD4 R1.1. BIOS F9 from 06/25/2010. Though that reminded me about another problem I have. If I run the @BIOS update utility the computer will BSOD. This used to work fine, but at the same time everything else started to break down, I got instant BSOD if I tried to launch that program.

Edit 2

I'm gonna keep adding to this question for every time I experience another damned and forsaken hardware glitch until I get a satisfactory answer/solution to this.

Today, the computer ran through POST then black, just black. Everything appared to be fine, except no video signal... reboot. same thing, but this time the POST screen never appeared. After a minute or so the video signal came back. I checked the cables, didn't find anything that indicated a loose connection.

I'm placing a order for a new mainboard today.

When you say that you've "reinstalled everything" I guess you mean that you have reinstalled Windows as well. Otherwise, to start again with a clean Windows registry would be a good idea to rule out software errors. A corrupt registry can lead to blue screens as you mention, but not the graphics problems you describe, from my experience.

A standard error searching algorithm is to disconnect everything but the bare minimum (a RAM stick, a hard drive, graphics) to run the computer and see if the problem persists. In this case I would suspect the motherboard, as you do. The only way to isolate that completely is to either have access to offline testing equipment, or having another equivalent motherboard where you can mount all your components and try to run the system.

If you buy a motherboard, you could always test it and see if it solves your problem, and return it otherwise for your money back (if the store implements this policy, obviously. Pretty much all stores where I live do).

Use BlueScreenView to analyze the dumps.
BlueScreenView highlights the drivers on the call stack, which can point to the malfunctioning hardware.

Also, do you have any errors in the Event Log?

If you have a serial port, a spare computer(ideally a laptop), you could connect the computers together via said serial port. When booting the computer that BSODs, press F8 and load Windows in Debug mode. The client computer with windbg running and configured correctly should connect to the BSODing machine. Then repro the BSOD on the target computer (if no solid repro steps, use it until it occurs again), then, once repro'ed from windbg, type

!analyze

This should give you the infracting modules/assemblies and point you in the right direction.