I have an HP ze4500 laptop which was having intermittent power failures when on battery, so I've been using it plugged in for a while and it worked fine.

While plugged in, it suffered a power failure and I didn't smell any smoke.
Now, when I push the power button, the LED's light up, but it shuts off again after 1 second.... it doesn't even get to POST.

I tried removing the battery, holding the power switch for 1 min. and booting from a/c only, removing the ram and letting it sit for a couple of days... you know, tips you find on google, but nothing works.

What could it possibly be? Motherboard or power supply?