First post here. I've been having this problem with my PC for a while, thought I'd ask. I've been searching various forums for people with problems similar to mine, but couldn't find anything similar.
I have a custom built (or as custom built as you can get in India, anyway) rig. I got it around 2.5 years back. The specs were-
Processor -Intel Core 2 Duo E7400 @2.8GHz
Mobo - Intel DG35EC
GPU - Galaxy 9800 GT (1 GB)
Windows XP SP2
The power supply is sort of a native product - it came supplied with my case, and I didn't think to change it back then.
Started off with 8 GB RAM, but had to cut it down to 2GB over the last 2 years, since the RAM slots seemed to be messing up. I assumed it had something to do with the hot weather, so didn't do much.
About 2 weeks back, my PC started having funny phases, turning off while booting, occasionally not booting at all. Everything else worked fine, so I didn't think much of it.
Then a week back, while playing MW2, after a couple of minutes, it completely froze up, with a looping sound. Soon it turned into a bunch of random colours/lines. Couldn't do anything besides turn the PC off from the mains. It'd work fine after that, so I assumed it was MW2 messing up.
Then it happened with Black Ops. And my PC took a turn for the worse. Wouldn't boot up at all. I removed the GPU, and it started booting normally again. I assumed my GPU was gone.
I tried playing Deus Ex (the original) on integrated graphics, since I assumed it'd work fine, and it froze up on me, same problem, monitor showed no input. I don't think it's overheating because the temps seem pretty normal (for India, at least) and the CPU heat sink is clean.
I initially suspected my PSU was failing, and so I changed it. PC still refused to boot with the graphics card inserted, booted fine without it. I tried running Deus Ex again, same problem, random colours, then monitor showed no signal.
I'm pretty sure it's not overheating, since I just cleaned the PC. I've run Memtest, didn't show any problems. So the only things I'm left with are the CPU and the motherboard, and I'm not quite sure how to diagnose the problem.
Given the age of the system and your report the environmental conditions may have already degraded areas of the MB, I would suspect things are continuing to "go south". If a new system is out of the question, you can probably find used pieces (MB) on ebay. I would try to avoid local shops as what they have may have the same types of exposures your system has had.
The ratings are similar or higher than my previous PSU, so I assumed it'd work fine.
The bit I don't get is, when I install the graphics card, it refuses to display anything. No errors, no POST beeps, nothing. The moment I remove it, the PC runs fine (except when I try to run a game, cue crash in 5 minutes). I think I can rule out a corrupt windows installation. Would bad drivers prevent the PC from booting at all?
If you have more than one slot you can install the card in it to test the slot. Also do a close inspection of the slot with a magnifier. Look for blackened, bent or broken contacts. Your point is right on. So if it works with no card and fails with the card, then:The card is bad; the installation is incorrect (are you using the additional 2 6 pin connectors); the slot/MB is bad or the power supply is not providing the 2 6pin connectors with the correct voltage. Not to say the problem is not just one of these but I thing this covers the choices.
Okay, an update. I tried changing the rendering settings on Deus Ex, from Direct3D to their own renderer, and it's working fine now. No crashes, nothing. So I guess Intel's integrated graphics mess up with Direct3D or something. It's probably my GPU that's gone bust then.