That model dates from around 2006. (found a post about it dating from Jully 2006)
Do you still use the original battery? If that's the case, that battery is probably dead and can no longer keep it's charge.
You need to get a new one.
If you use the adaptor/charger, make sure that it's properly connected both in the wall socket and the computer's connector. Check that the adaptor's cable is intact.
If the cable is damaged, you may need to replace the adaptor.
Electro, March 2012
