Asus Motherboard won't power up

[Skullbones]

To make a long and frustrating story as short as I can. I bought a custom built computer with an ASUS P4P800se motherboard with an Pentium 4 2.8 ghz processer. I got the computer and it worked fine for 6 days. After 6 days I went to boot it up and it would not turn on. Even though it worked fine when I last powered it down. I went to a computer repair place and they said that the power supply must be bad because they tried it with their own power supply and it worked. So I sent back for a new power supply and when it arrived I hooked it up and it still would not work. (The power supply is a 400Watt ATX power supply and by the way, the green light on the motherboard is lighting up when I plug it in.)
So I say, "okay, it has to be the motherboard then." To make sure the problem is the motherboard I take the motherboard out of the case and hook it up to nothing but the new power supply. I try to jump start it by touching the two metal pieces together and it still won't power up. Like always, it is completely dead. So I send the motherboard back to the company and they test it and says it powered up fine for them. I cannot believe it. This seems impossible. What is going on!?
Does anyone have any insight into ASUS motherboards that the computer won't power up under a certain condition? Is there something i'm missing here because this is not making any logical sense and I don't know what to do now.

[Cricket]

Try clearing the CMOS. Remove the motherboard battery for half an hour.

Are you sure you were touching the right set of pins on the front panel header?

The little green LED on the motherboard only tells you that power is reaching the motherboard from the PSU, it doesn't mean the PSU or motherboard are working properly.

Cricket

[Yuanji]

just wondering, what brand is ur PSU?

[glc]

To jump start it out of the case, the CPU fan must be plugged into the correct header and you should have ram and a video card installed. The P4 power connector (the little 2x2 plug) must also be connected to the motherboard.

Otherwise, I'd suspect another dud power supply, all power supplies are not created equal.