Laptop keeps restarting

I previously posted this in another forum, but am now thinking it is a hardware problem. This is the thread: http://www.techsupportforum.com/f10/solved-notebook-wont-start-494850.html

Basically my laptop keep restarting itself, asking me what to do in a black screen, then showing the black start up XP screen and then crashing and briefly showing some blue error screen. This keeps repeating itself. I tried normal start up, last known configurations and safe mode, but either way it can't get past the black start up screen.

When it was still working, I didn't look at the light signal that indicates whether it needs power or not, and I just keep the adapter plugged in at all times.

I tried to load up completely and kept it plugged into the adapter untill the red light indicating it needs power turned off. Then when I tried to start up, the adapter not plugged in, it was low on power within no-time. The adapter is tested and is still working.

Is it the battery? What else could it be? Should I just replace the battery or is there anything else I could do?

This is the type of laptop:
Packard Bell 63295 PL EasyNote C3255
Microsoft Windows XP
I purchased it in 2006 and have never cleaned it yet. It got pretty hot sometimes.