Computer hangs at random points on boot, GPU possible culprit

[salisian]

My computer is possessed, and I'm not entirely sure what forum to put it under, as I have some unknown number of parts with unknown errors.

I built my own computer, and it worked fine, with a few little oddities here and there (and about one weird blue screen every couple months,) for three and a half years. I went on vacation over December, unplugged and covered it, came back, plugged it back in, and turned it on. I got into windows, was watching videos, and the computer froze in such a way as to imply my GPU had overheated or failed. It then failed to reboot correctly.

I opened up the computer, checked all the wires and jumpers, blew out errant dust (just in case), cleaned contacts, re-seated components, closed it up, rebooted, and it worked fine. I played graphics-intensive games, and everything was great. Then I shut down for the night.

The next day, it failed to boot again, hanging on the windows loading screen. I powered off and rebooted, and it didn't even get through POST. Each time I tried to boot my computer up, one of several things would happen, chosen seemingly at random: 1) The computer fails at POST (external fans spin up, lights come on, but no beeps, no display) 2) the computer manages to complete POST and gives the sequence of beeps to indicate "No VGA found", and the "No VGA" light stays on, 3) The computer gets to the windows loading screen and freezes.

Attempts to get into BIOS fail: either the computer entirely ignores my hitting delete, or it registers it and then hangs on a black screen with a blinking cursor.

I moved my GPU into a different compatible PCI slot, and it booted up correctly. I got into BIOS and all the settings were fine. Then I got into windows, tried to remove the old GPU drivers and install new ones, but neither nVidia experience nor windows update could manage to do it. But I ran windows update anyways, and when it tried to reboot to install updates, it hung again. The cycle began anew, with the same three possible outcomes for each boot.

What doesn't make sense to me are the random failure points, and the fact that it's managed to get to windows successfully multiple times at this point.

I don't have a handy GPU around to test with, and my motherboard has no on-board video. Several signs point at the GPU, and I'm willing to accept that that's the problem, but why would it randomly decide to function at high performance? That's the question that bothers me (if it is indeed the GPU's fault.)

I'm a mid-range user with a fair amount of electronics/electrics background, but I'm now pretty much out of answers. Thanks in advance.

CPU+CPU cooler: AMD FX-8350 Black, Cooler Master Hyper 212 EVO
Motherboard: Asus M5A99FX
Ram: G.Skill Ripjaws X Series 16GB (2 x 8GB)
SSD/HDD: Samsung 840 Pro 128GB / WD Blue 1 TB
GPU: GeForce GTX760
PSU: Rosewill Capstone 750W
Chassis: Cooler Master HAF 922
OS: Windows 7, SP1

Edited: More system specs

 

[Lutfij]

There might be more happening here. Might want to list your specs like so:
CPU+CPU cooler:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:

Are you on the latest BIOS revision for your motherboard? Have you made sure you've backed up your critical content and reinstalled your OS after recreating it? A corrupt installer can and will be the bane of optimal computing.

 

[salisian]

I reinstalled Windows 7 about a year and a half back as part of the usual computer maintenance. At this point, though, I'm pretty sure I can't even get the system stable enough to do so again.

As for BIOS revision, I haven't changed that for a while, but at this point I also don't know how I'd check it.

How would either of these two apply to the situation at hand? (I'm not challenging, just curious how my computer could behave so randomly in such a situation.)