Shut down after 3 seconds

So I have an Abit mother board with a Phenom Black Dual Core AMD Processor, I'm using a 750 Corsair Power Supply.

I was doing diagnostics on my motherboard because after installing a new videocard (GTX 450), the computer shut off one day and would not start.

When memory is installed in the motherboard (and nothing else) it shuts off after 3 seconds. However, when I take the memory out power stays on throughout the motherboard but it does not boot. I tried 3 different memory sticks 2 that where in the computer when it first shut down- but 1 that was off to the side (so theoretically this memory stick could not have been affected). There was a brief period when I installed the MB into a new case and even with the memory installed the entire board got power but it still did not boot.

It seems like there is some kind of imperfection where the memory is plugged in- but I don't know why installing a new video card would have created or exacerbated this problem.


Any thoughts?