Help me! computer will not POST

My computer was a athlon 700 with an abit KA7 MB
It ran fine for a year or so when I came home to it one day to find it off (which meant the power had gone off) and when I tried to turn it on the fans, and lights came on but the screen stayed blank and the had drive and cd rom Busy lights came on steadily..
I turned it off and pulled out one of the USB devices in the back and turned it back on. This time if powered on fine.

it worked great for months after only until one day I powered it off for a long period of time. when I went to turn it on again it did the same thing. I tried everything to get it to turn back on but nothing worked.. I stripped it down to the vid card processor and fans and such and still no luck.

I just recently replaced the mother board and processor and vid card. But it still is having the same problem.

Could this be the powersupply? And could I have damaged the new board by using the old powersupply if it is faulty?
Everything powers up ok.. but the POST won't start and the IDE acitivity light stays on..

Help!

I did that even. Nothing.
I even ended up replacing the power supply.. But only after I tried to boot it with the new MB and proc using the old power supply.
I think I might have burned up the new processor and MB with the old supply though

If the power supply is bad could this have happened?
I've basically replaced the entire system..

Also the new processor heats up really bad within a minute..
The heatsink is hot to the touch in less than a minute. I know that can't be good..
it's a 1.3 gig athlon on an Asus A7V133 MB..

using an older psu with a new board can cause a lot of problems... lack of power is y many athlon systems just burn out....only thing that really gets damaged is the board...i've had this happen to me...most likely your cpu is ok.....but your board might be dead....try gettin' your processor tested in another board and that will give you your answer

Nice people are kool...Mean people just suck