Hi, I'm trying to figure out what is wrong with my computer!

I got a new case (Enermax with 350W PS) and transferred the motherboard (Athlon 800MHz), drives etc. When I turn on the computer, the power seems to be connected fine (fans come on, DVD drive opens, etc) but that's about all that happens. The monitor "wakes up" as if detecting power from the video card, but can't find a signal and goes back to sleep. And (my main diagnostic tool so far) the keyboard LEDs flash on but then go out and won't come on again. This is how I know something is really messed up. If I unplug and re-plug the keyboard, the lights come on for an instant but then go back off. So obviously I get no BIOS messages, beeps, floppy drive whirring, or whatever.

Here is what I've done so far to isolate the probem. I've removed all three expansion cards (PCI network, sound, and AGP graphics) and even with the graphics card out it appears to do the same thing, and the keyboard behaves as described above. I've also disconnected the hard drive. So how can I tell what's wrong? When transferring the motherboard, I did remove the CPU from its seating and used a thing piece of cardboard to clean mad dust from between the fins of the heat sink, so maybe i damaged it, but otherwise could it just be not seated properly? How can I tell if the CPU is messed up?

Any advice or links are helpful. I've looked at lots of troubleshooting links but none mention this specific situation (again, identified mainly by the behavior of the keyboard lights).

thanks!

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It is unlikely that cleaning the heatsink with cardboard could damage the CPU in any way. On the other hand electrostatic discharge could, were you well grounded? It is also possible that you installed the board with a short, so you may want to take it out of the case and try a minimal config on a nonconductive surface (like a wood table or piece of cardboard) to see it you can get POST. If you have a way to check the power supply to see if all the legs are ok, it might be worthwhile to do so, particularly the 3.3 leg. I would also check to make sure the CPU is properly seated and that the CMOS clear jumper is in the proper placement.