ladybridgeport

I have a Toshiba Satellite Laptop Running Windows XP Pro v. 2002 (non 64-bit version) with sp3, problem occurred with sp2 also, Mobile Intel(R), Celeron(R) CPU 1.5 Ghz (2 chips totaling 512 Mb RAM).

Hardware history: Replaced factory hard drive that went faulty with a refurbished faster hard drive. Toshiba sent a replacement RAM chip because some were reported faulty, I never sent back the other so both chips are inside instead of the one that came preinstalled with the computer.

Whenever I view videos for a long time or my computer is working hard for a long time, my laptop shuts off. Normally when my laptop is off, a standby charging light is illiuminated for battery charging. When my computer shuts down without warning, that light is not illuminated and I physically have to unplug the AC adapter from the back of the laptop and plug it back in, then the light illuminates and I am able to start the computer again. If I leave the computer alone for a few hours, the light automatically comes back on without unplugging and plugging it back in. What is wrong with my computer?