The machine can't POST if the CPU is bad. You also need working memory and a video adapter (built-in or separate card) installed, if either of those is missing all it will do is beep. The fact that you get no beeps (the case speaker _is_ connected to the mobo, isn't it?) seems to point to either the CPU or motherboard.
Your first power supply was almost certainly the cause of your problem. The trouble is that when a power supply goes bad it sometimes takes other components with it. The motherboard is the most likely victim.
If your confidence and experience permit, you can pin this down by substitution. First, test the memory module(s) by temporarily installing them in another motherboard. If they work, then you can test the CPU by installing it in a compatible, working motherboard. If it works, then the motherboard is the only thing left, it must be damaged.
Compaq motherboards are proprietary, so you would have to buy a replacement from them. Their website would have information in the Support section regarding your model. Good luck.
Edited by DaveM59, 08 June 2006 - 09:17 PM.