|Have you, or is it possible someone else who had access to this computer...|
- dropped it, or dropped anything on it, or otherwise exposed it to a physical jolt ?
- spilled liquid on it, or sprayed it with liquid, or exposed it to liquid such as rain ?
Since the computer last worked properly all the time, has there been a power failure event. and/or lightning strikes in your area, that happened while the AC adapter was plugged in ?
Those things are the most frequent reasons something inside the laptop has been damaged.
Laptop batteries can develop internal shorts when they're older.
An internally shorted battery can cause your problem.
Try removing the battery and have just the AC adapter plugged in when you attempt to boot the computer.
Installing ram that isn't compatible with using it in your mboard, or the ram not being seated properly, can cause your problem.
Have you been fiddling with the ram since the last time the computer worked properly ?
- if this problem happened after you changed which ram modules you have installed, try installing the ram modules it had in it previously when the computer worked fine.
- if this problem happened after you had removed and installed ram modules, make sure they're installed in the proper direction and are all the way down in their slots.
You MUST remove the battery AND unplug the AC adapter whenever you plug in or unplug the ram modules, otherwise you can damage the ram modules or the ram slot circuits or both.
(If you have installed any ram module backwards in it's slot, when you attempt to boot the computer, both the backwards ram module and the slot it is in are fried instantly and niether can ever be used again.)