I need to single out faulty hardware

[Kalmah]

I don't have anything to swap the parts out with.

My computer wont turn on and off with the power or reset button in the front. It's stuck on. I can only turn it off by unpluging or swithing off the psu. When I switch the psu back on everything powers up without having to push the front power button.

Everything seems to get power; mobo, fans spin...
The system doesn't post. The monitor doesn't get a signal. No beeps.

I've stripped it down to barebone. I even put it in a different case to make sure it wasn't the power button circuitry. I tried several video cards. I've removed the cmos battery, waited 20 minutes, then replace it.

The computer quit working when I put it in standby for about an hour. When I came back it wasn't in standby anymore, it was on, with a blank screen. Power and reset button not working.

So what is it?

psu
mobo
cpu

Can I take the psu off the list of possible problems?
Add anything?

I appreciate it.

 

[amdskip]

My vote is power supply but what power supply do you have?

 

[Kalmah]

It's a Coolermaster 550 watt. (that's all that I can remember, don't know about a model)
I remember that it wasn't cheap.
Motherboard is getting power, all fans are running.