I have had a couple of machines that exhibited similar problems.
You have to be methodical.
Unlikely to be a drive but could be M/B, ram, or power supply giving up the ghost - maybe the processor but that is not easy to replace.
Unplug everything and see if it exhibits the same symptoms with just the power supply, the motherboard should bleep (if there is a case speaker) or at least stay on.
Change the cmos battery (cr2032 in supermarket) and reset the bios - read m/b manual.
Try again.
It could be oxidation on the contacts of the ram sticks.
I would suggest you then try starting the machine with tthe absolute minimum - 1 stick of ram, graphics card and see if it exhibits same symptoms - should bring up the Bios screen.
If it works then start adding the other ram sticks one by one.
If it doesn't then try a different ram stick.
Add ram sticks one by one.
Still no go, then you have narrowed it down to the graphics card or power supply or a failing motherboard.
Pick whichever - you could try with a cheap graphics card to narrow it further.
If it's any consolation both my problems were 1 m/b and 1 power supply.
Last edited by finncapt; 18th Aug 2014 at 13:28.
Reason: complete rehash