Hardware

The problem may not be the motherboard but the graphics

Boot the computer,when startup screen appears,push the button to enter bios setup,disable the onbaoard graphics,now install a pci or agp card in one of the slots to see if you get video.

Mkae sure that memory in seated in slots properly

When you turn on the computer are you seeing anything on the screen while it boots? If not, do as suggested by the previous post, but install a stand-alone graphics card first.

Did you check if the CPU is firmly in the slot?

Questions:

Do you hear any beeps? Do you have power lights power supply and other fans spinning etc.

Download the manual for the motherboard.

Reset the BIOS folowing the instructions in manual. After resetting and depending on the Compaq system you may need to download the BIOS operating software.

Try plugging power directly to the wall outlet.

Disconnect everything from the board. Only leave the memory and see if it boots. If so re-install devices one at a time until failure occurs.

As mentioned you can install a video card to see if it boots that way.