Once i unplugged all drives and such the computer powers on

What Pavilion is it?

Sorry

a6400f PC

Thanks

Try unplugging everything and plug in JUST the 24 pin (big main connector) and the 4 pin. Boot and see if it fires.

Ok
Did that but nothing unplug the 4 pin and the fans power supply will start after a couple of seconds, the lights on the dvd light up and the hard drive seems to be working but I get no screen. BTW the monitor is not hooked up when testing. Unplugged the monitor and plugged it back in and it reset itself but shows no signal.
MOBO nfg?

What power supply did you get? It would be easier to exhahnge the PSU to make sure you didn't get a bad one before pointing the finger at the mobo. I'd try exchanging the PSU. If it doesn't fire on a new PSU, I'd say the mobo is indeed shot.

OK
Here is a dumb question I thought a PSU was the power supply unit? Then what is the PSU I bought a brand new Power supply from a surplus store, like I said everything powers up but that 4 pin plug, What is that pin for?
Thanks again for all your help.
Marty

Another note If it is the MOBO what should I get? I am not that good with computers yet but give me some time with this and I will!
Marty

Yes, PSU is power supply, and just cause you bought new doesn't mean anything, there could still be something wrong with it. Case in point, I just bought 2x4GB DDR3-1333 SODIMMs for my wife's laptop and am currently running memtest+ on each stick individually, cause when I have one stick in (4GB) everything is fine, but the other stick in I keep getting BSODs, so each is getting tested individually and I suspect that I will be RMAing one or both sticks by the time it is through (HP laptop, chipset and HP site allow for 8GB RAM).

Near as I can tell, A) The PSU has a problem with the 4pin ATX power (the 4 pin provides power to the CPU socket, so unless you took the CPU out lately and bent pins, I'm guessing we can rule that out), OR B) The plug on the motherboard got spiked or some other anamoly happened and now it isn't accepting power FROM the PSU.

That's why I am thinking take the PSU back, get another and try it, it is the easiest and fastest way to diagnose. Not all PSUs are of the best quality, thus I was wondering what one you bought. If it was an Antec or Corsair, something higher end, I would be more prone to lean toward mobo problem. If it's some Kingwin or lower quality, it could be the PSU.

Let me know what brand and how many watts it is rated for and I'll see what I know about it. I would still consider taking it back, but after I find out what one it is, I can direct you toward a better or same PSU to excahange for.  

As for what motherboard, let's cross that bridge when we get there. HP uses proprietary gear on a lot of their builds and depending on what motherboard it is, you might be better served to get a whole new computer, as the 'custom' motherboard HP will try to sell you will be more expensive than a whole new system!

PSU IS a Hercules 600w 12 cm fan, I live in Hawaii and parts are scarce I got this one from a supply place in California off E-bay it was celophane wrapped and no burnt electronic smell. I talked with one of my customers today he is a gamer and I mentioned it to him and he thinks it is the cpu that it got hot the night i left it on and the cpu got hot and shut it self down, (because of the humidity here I usually leave it on all the time to stay dry and not rust) He told me to remove the mobo and gently brush and vacumn the board off then remove the heat sink vacumn the cpu and remove it and replace it replace the heat sink grease and try it, I will have to do it tomorrow as I have no time to do it now. Will report any progress if any
Marty