What could be causing random shutdown/reboots in a PC. Recently i've been trying to re-install windows and linux on my pc as its been very tempormental lately. At the moment i can't even install an OS as it seems to either shutdown my system half way through or hangs. Its not the cd's or cd drive i've tried a lot of alternatives so i'm down to either memory/cpu/mobo Is it possible my power supply just packs out? What do you guys think I'll be trying with some RAM from work this weekend see if that makes a difference.

Well it sounds like you got the RAM issue taken care of (or at least soon) so thats a good start ! That just leaves the mobo or powersuply of the two its probably your powersuply. If its your mobo the cause would be bad caps on the bourd you know what a capacitor looks like ? well if you do (if not pictures on the net lol) Look for bulgeing or leaking caps and discolored stains on your bourd... If you see those then yeah its your mobo hmm although not seeing those is not a promise its not the mobo lol

Edit: I just seen on another site some one with a simular problem and the problem turned out to be a bad IDE cable to the HD... Just something to check I guess

My main problem was clock speeds were too high as I overclocked my system. I doubt it's that though, but try UNDERCLOCKING it a tad. Heat will also cause that issue as with most processors there's built-in safety features that, if the processor get's too hot, it'll shut down to keep from burning up.

Not enough power could be another issue. Try unhooking everything you DON'T at the moment, then try.

And if you can test the RAM later, that'll be a good start too.

What is the rating on your PSU and how many components do you have connected to it?

Ok well it seems like i finaly figured out the cpu was over heating and shutting down due to the safety mechanism. Had to take the fan off the heat sink and found a thick layer of dust that was stoping any air flow to the cpu and causing it to heat up. Cleaned all that out and seems to have come back to life.

Thanks for the suggestions above they all helped narrow this down.