RE: Beep Codes
Four beeps indicates a memory error - three is a mainboard failure.
Unplug the system, remove the battery (or disconnect it ) and hold the power button for 30 sec. Remove and reinstall both memory modules and try powering up -- if you still get nothing, try one module at a time until you isolate the bad module (replace) or bad socket (replace the mainboard).
If you get a 3-beep/no start sequence, the mainboard is bad and will need to be replaced.