Urgent, really bizzare problem.

I bought myself a new video card, the ATI Radeon x1600 Pro. It's going inside a Compaq sr2006nx tower, going to wire the new card up to my TV and the on board graphics to the monitor.
Dual screen, one of which would be a TV. That with the ATI remote I have, it'll be awesome.
Anyways, I installed it yesterday, fired up the computer, installed all the drivers and such. I left it on overnight, that's what I always do, but today when I got home, the computer was off. And cold, the shutdown must have happened hours before.
I pressed the power button, nothing. It just sat there. I unplugged the computer, plugged it back in, and pressed the power button. I got half a second of life out of it, the LEDs and fans turned on, then turned off. Then the computer wouldn't turn back on, untill I unplugged it and repeated.
So I then tested the power supply by shorting out the green and ground wires, and hooking up an LED. It worked perfectly. I plugged the computer back in, and pressed power again... I got a second out of it, same as before. It keeps just giving me that second, after unplugging and plugging it back in.
Now, I tried to take out the video card... and behold - It worked! I put it back in.. same thing. Took it out again, and worked. I guess this issue STARTED with the video card.
Anyways, I asked around, and people suggested that I got a higher wattage PSU. Mine was 160 Watts, appearantly that's really really bad. I went out today and bought a new 500 watt one.
I came home and installed it, it fit perfectly, I connected every thing up, and I had the same EXACT thing as I did with the old power supply. I took out the video card (and here's where it gets weird), and it worked.
It worked without me even touching the power button. I figured it's a generic PSU, it has a switch on the back, maybe that's why. So I plugged in my moniter into the onboard graphics, and the monitor just sat there.
I got an orange light on it, meaning it's plugged in with no signal. I put in the old power supply, and reverted everything back to how it was originally, exactly how it was. I plugged it in, and the power button didn't work!
This is when I figure out that something is REALLLLLYYYY messed up. The screen still won't work. I thought I would try to log in remotley, I have a program called logmein, that allows me to take control as soon as it's online.
I went to take control, and the computer showed as offline.

So my question is, what is going on here?

There's a video of it right here:
http://rapidshare.com/files/81628838/Movie_0005.rar

 

Welcome to MajorGeeks! :major
Sounds like the motherboard died. From the description, I'd say your PC was pretty old and those old stock power supplies were complete pieces of :crap... the new video card was probably just too much, it may have tried to pull too much juice from the weak power supply, which in turn fried the board.... this would explain why the power switch doesn't work any more and why the on board video doesn't work any more; the motherboard has died. Nothing personal, but this is one reason why I always tell people to turn off the PC when you leave the house or if it won't be used for over an hour. Even a power surge could have done the damage you describe; if the PC is off, a power surge can't do anything.... testing a power supply with the old paper clip and LED doesn't mean it's working. It simply means it's kicking out enough juice to power an LED. You can use a AAA battery to power an LED.

 

I was fearing that. I was trying to not think it was that, but shit, I'm screwed. I can't afford one of those.
The PC wasn't old, actually, about a year. Warranty JUST ran out 20 days ago, too.
Anyways, maybe I can find a replacement mobo online somewhere. I'll try and find a cheap one.

 

try to reset the CMOS by pulling out the little battery on the motherboard and keeping it out for a little while (10 minutes) then put it back in and try to boot up again. But yeah it does sound as if your motherboard died, the same thing happened with my Sony VAIO