Hey Nev,
Thats what I thought too, so I changed out the psu for a new one (a more powerful one in case that was an issue). I switch it on, it powers up, the fans do start up, but thats as far as it goes, no beep, no drives kicking in - it stays like that indefinitely too, tried leaving it a while, but nothing.
Even changed the cmos battery, I'm at a loss as to what to do now except get a new motherboard and rebuild!!! That's the only part I can think is at fault now, having checked all the others that may cause boot problems.
Very frustrating!