No, hadn't tried it before. I was pretty certain it was a faulty mobo in the first place (and still am), so when i fitted the new one, i just connected everything up in one go.

Just tried a barebones boot, but still no bios screen. No nothing.

Dad thinks i should take it into a shop to be looked at - he's fed up of me 'borrowing' his laptop all the time, lol - but when i took it in before, the chap had no suitable AMD motherboards on hand, and no CPUs, either. So there wasn't much he could do. And if i take it in again and he still doesn't have everything he needs to do thorough test of all the parts, there's not much he's going to be able to do that i haven't already tried.

give the guy a call before you set off to his shop for the pc check up and ask him if he has the equired stuff to test your system on. Lets hope he s able to find the issue with it.

Raj

Ok, took it to the shop. The bloke there tested everything i had already tested, and concluded it was the motherboard - again. He had a new AM2 mobo in stock, so i asked him if he could fit that for me. He did (it's my third mobo if anyone's counting), and it's sort of working again.

I say 'sort of' because, after it has been left on for a certain length of time, even just idling, it'll suddenly shut down. If you try to turn it back on straight away, it'll promptly and unceremoniously shut down shortly after the BIOS screen.

Right now, i'm thinking it might be an over-heating problem. I've noticed he's put my cooler heatsink-fan on backwards. I have an Arctic Cooling Freezer64 Pro on my CPU, and he's put it on so that it is blowing hot air in towards the centre of the case, instead of out towards the exhaust fan at the back.

Does that sound like a reasonable hypothesis? Would such a seemingly minor oversight give rise to such serious effects?

This problem occurs maybe 10 minutes after turning it on, which means that the machine remains essentially unusable.

I'm not a happy bunny, but a sad panda instead.

Additional hardware normally proceeded by change of power calibration of your PC.
Maybe you need to buy new power supply. A higher power supply will solve your problem

First things first your problem started when you plugged-in your DVI connector, you may have pushed the card to hard and it, extracted the card little bit thereby causing the card to improperly sit in its cradle or connector and if you can see how close it is spaced a lot of things can happen , as you may know a portion of your on -board memory has an allocation for video aperture and as you push the card to hard some pins shorted and caused oddballs of problems i have encountered this when i set up 40 units of computers on a networking using not utilizing the built-in lan but lan-cards-when one of my guys excessively push the UTP connectors to hard the card push up SHORTED the CONNECTORS and caused mostly with those low quality casing, and shorted 3 units of motherboard in a row, and also cost me 2 memories.,Im sure your memory sustained a secondary breakdown where-in it is intermittent try isolating the one from the other if you have two. LIFE IS LIKE A CLASSROOM WHERE EXPERIENCE IS THE BEST TEACHER FOR ANYBODY WHO IS WELLING TO LEARN.

Those are some interesting suggestions. Thanks, guys. I appreciate it. I'm going to focus on cooling for the time being, if only because a case fan is cheaper than a new PSU, lol. But if the problem persists even when i've got it running at a reasonable temperature, then the power supply is something i am going to have to have a look at.

As for the RAM chips, i have bought some new ones, and those are the ones i currently have installed. I'm going to be using the old ones in my next build, though, and if that system gives me problems, then from what you say, the RAM sounds like it's going to be the place to start looking.

Does it it give any beeps on POST.
These usually indicate the fault.
However,they do vary according to the BIOS .