RE: BIOS Boot Fails
Unplug the system, remove the battery and hold the power button for 30 sec. Remove and reinstall the memory modules and the hard drive.
Check all the USB ports for bent pins - a short in a pin inside the USB port will kill the POST sequence.
Try powering up on AC only - no battery. If it will, the battery is faulty.
If no power up, try one memory module at a time until you find the faulty module or socket and replace the module or the mainboard once you identify the faulty part.
if the memory tests OK, remove the hard drive and try powering up -- if the system will, replace the drive with a new one.
Failing all that, replace the mainboard.