BleepingComputer.com: Desktop will not boot

Recently, I opened up my computer to switch out a video card, add some RAM, and generally just look around. Now, the computer won't boot at all. When I push the power button, I get no monitor output at all. The light on the back of the PSU blinks once very briefly upon attempting to boot, and then powers down less than two seconds later. When this happens, the power indicating light goes off and will not come back on unless the PSU is unplugged for about fourteen seconds and then replugged. This is the same amount of time that it takes for the light to go off after being unplugged.

I don't believe that the PSU is the issue, as I've tested it in a computer made up of odds and ends, in which it worked just fine. I removed all unnecessary hardware and got the same result. I tried removing components and checking to see if there was any visible damage. The only thing that I saw that might have had an affect was some residue on the CPU. It was bluish and sticky, a bit like what you get when you rip off old duct tape. Upon pressing the power button with the CPU removed, I found that the PSU light did not flash and the computer did not power off (although obviously it didn't do anything else, either).

I'm reluctant to buy a new CPU because I'm not certain that the CPU is the problem and I'm not very experienced at diagnosing hardware problems. Any help would be appreciated; thanks in advance.

What kind of video card did you buy, and what is the model of your PSU?

The new video card is an ATI Radeon 9600. PSU is a Delta DPS 250QB-4A.

Who made the video card, and can I get the model number?

Are you certain that the RAM you installed is the correct speed and is it good? what happens when you remove the RAM and turn on the computer as it was before you added new hardware?

Also, the substance on your CPU: was it heatsink compound?