Computer has gone pear shaped

[u8myufo]

It started a couple of weeks back now with the pc just shutting down on its own for no reason but not very often.The problem was the fan on the graphics was sticking like mad and I had to take it off and stick another one on. All seemed fine for a while but today it was just getting worse and shutting down whilst using nothing in particular, programme wise. It would only start up if I switched the power button off on the back of the machine and waited a short while, but now when starting up I get one post bleep and then instantly it powers off. So does anybody have an idea where to start? I think that maybe the card was damaged in some way, failing that I suppose power supply would be my next port of call.
Any help would be much appreciated thanks.

[Midknyte]

Check the motherboard for bad caps.
http://www.badcaps.net/

[u8myufo]

Thanks for the info, I have just discovered one of the memory modules is shot. I can now get system to start and goes past post beep. However this brings along another problem, system boot failure, insert installation disk and press enter. After doing that nothing happens, the message is still there along with just a flashing cursor. I have it set to boot from cd, and even if I shut down and re-boot with cd nothing happens.

[Shinma]

May want to state the components making up the system...
Unless it is the one listed in your signature.

[whutsupdoc]

check the cables to the hard drive first, maybe the cable got loose... otherwise hard drive failure.....

[xmrb2003x]

Is the new fan on the graphics card spinning properly? If not that could be overheating. You could try a different graphics card because I've had that before where my graphics card was on the way out and my pc wouldn't boot properly because of it.