PC crashes

[bren4q]

The PC I put together about 4 years ago has been crashing more and more frequently over time. It is practically unusable now. I'm getting a new machine soon but this one is still good when it works so I reckon it is worth fixing as long as not too pricey.

The crashes vary from blue screen hardware errors, to reboots, to lock-ups. I've done a fair bit of trial and error testing on various bits and I think it's a motherboard fault, but any other ideas (particularly if they are quick tests) would be welcome.
One unusual thing was that if I managed to get something like Skyrim running, it would often run for hours without a problem. But something like opening a new tab in Chrome could crash it. Being left idle for a few minutes on the desktop or login screen was also a sure fire way for it to lock up.

Things I've tested -

Software/drivers:
I have 2 installations of Windows on the machine yet both have the same problem, so I think a software/driver issue is not the cause. I updated video drivers on the main OS anyway, but same crashes.

Graphics card:
I swapped graphics card for a different one. Same crashes.

Power supply:
I swapped power supply for a different one. Same crashes.

Memory:
There are 4 memory sticks. I took out 1 pair and ran with just 2. Same crashes.
I put those 2 back and then removed the other pair. Same crashes.

Hard drives:
I haven't tested anything on the hard disk. There are 2 in the machine. Usually a failing hard disk would be slow or clicking, which isn't happening. Sudden crashes aren't usually a symptom of bad drives.

CPU:
CPUs completely failing would be extremely rare I assume. I never overclocked this one.

Motherboard:
I'm thinking this is the culprit. But if it is, it means I have to disassemble and rebuild everything, which I'd rather avoid. I'd also like to be more sure that this is the cause before going ahead.


Anyone any other ideas of what I could check before buying a new motherboard and taking apart the whole machine?

[Skitty]

install a program called blue screen viewer. and when it crashes send me the logs.