PC Woes

[Daekesh]

Ok, so, heres the situation...  When I press the power button on my PC, nothing happens.  Uber

When I plug the power cord in and flip the PSU switch on then some lights come on on the motherboard.  The hey-i-have-power lights.  However, when I press the power button on the front of the PC or the one on the motherboard (it has one built onto the motherboard, too!), nothing happens.  This has been happening to me for some time now, but usually it starts up after Ive left it unplugged for a few minutes.  This time it seems not :\

Sometimes when I push the power-on button some extra lights flash on for a second and the fans sort of starts to go around a bit, but then stop instantly.

Basically, Ive narrowed it down to 2 possible things:
- Motherboard
- PSU

If it were anything else (gfx card, hard disks, cpu, etc) then itd turn on and simply beep at me, telling me whats wrong, so I think I can rule those out (to be sure I unplugged everything except the gfx card, cpu and ram - and eventually the gfx card, too) to see if it would turn on... nada.

I have no replacement parts compatible with the machine.  Ive tried resetting the bios.  Does anyone else have any ideas what I could try?  Or what else might be wrong?

Any help would be appreciated

[Gaeios(Graxlos)]

I had a very similar problem.
I replaced the psu.

[Kelrathos]

What Grax said. Exactly the same problem -> PSU deaded. New PSU -> HEYHOOOO SILVEERRR!

[delling]

In my experience, tempremental start-up is normally a power short somewhere.

Screws in too tight on a drive or something.

Tried unplugging everything except motherboard/PSU/keyboard/monitor?

(Funny, as we talk my computer is bluescreening and I'm trying to fix it...)

[Daekesh]

Well, everything except cpu/gfx card/ram, yes.  Should I try removing my ram and cpu?

[Smorisha]

Never ever remove CPU without actually having to. Every time u remove u should clean the socket and apply new gelly thingy so if u don't have it don't do it.
It smell like lack of power supply on one of MB inputs, just replace PSU or if u have any skill in electrical stuff test it with Unimer unit but yeah, changing PSU is best solution since its not expencive.

[Daekesh]

Well, there were 2 inputs on the motherboard I never plugged in (for whatever reason).  There was the normal 20 pin connector, the 4 pin (square) one and then there were 2 others... a floppy drive power connector and a hard disk power connector going directly into the motherboard.  Guess I missed them when I put it together the first time, but I've never needed them plugged in.