upgraded CPU and now no power

So I took the plunge and upgraded the CPU from 2.0Ghz core duo to 2.16ghz core 2 duo. Now I have no power and all that happens when I hit the power button is the light blinks once, shuts off and nothing happens. I have reseated the memory many time and I have even completely taken it apart and tried a second CPU of the same specs and still get the same issues.

Does anyone have a clue what could be the issue?

My last resort would be to take it apart again and put the old CPU back in to see if it boots and I didn't fry the board at some point.

I was really careful and even cleaned every thing out with a compressor because the thing was disgusting with dust build up.

Any help before I take a 3rd plunge would be appreciated.