HP DV1000 switching off

Hi everyone, recently my HP DV1000 laptop started to switch itself off, suddenly and a few times a day, it's on windows xp, 1gb RAM, 100gb hard drive, 1.73 Hz. It's about 7 years old now, but its motherboard was replaced 2 years ago because sth was wrong with the jack adapter at the time- it would burn the adapter all the time and would also switch off. But it was long ago, pc world people fixed it and replaced the main board.
Now 2 years later, every time I try to record a dvd or convert a pdf file into word or do sth else which is "heavy" for the machine, it seems to me the laptop overloads and just switches itself off. I must note it does not overheat and the ventilation is good too. No viruses found. The only thing I noted- when it switches off and then I switch it back on- the light for the battery(there are 3 blue lights on the front) is on- in fact all 3 lights are on, even though it is on the charger already. Any thoughts what could cause the laptop to suddenly switch off with no warning? Thanks!

 

Basically, you probably need a new mobo. It'll cost you about $50 if you swap it out yourself. Which isn't hard to do.

Here's the service manual: http://h10032.www1.hp.com/ctg/Manual/c00444244.pdf