CPU issues

Here is the issue:

My computer is off. I have just reseated my Heatsink to put a new THP on to cool off my P4 631. When I reassembled ther unit and plug the powercord inot the wall, the CPU think light comes on as yellow and I cannot turn on my CPU. It is a Compaq Presario SR2170NX Pewntium 4 631.
It's better to replace the Lithium battery - those things don't accept a charge after a certain amount of use. CR 2032 - a pack of six is under $10 at Sam's Club. The batteries are located right in front of the pharmacy counter (glucose monitor supplies).