You need to contact HP directly.
This is a known issue with HP laptops.
They have issued a bios fix, but it is not reliable at all. Basically you need the motherboard replacing on your laptop.
I'm assuming that it is out of warranty, BUT, search around in google because I'm pretty sure they extended their warranty for this exact problem, so best bet is to contact them, and say you have been reading up on what is a common problem, tell them you have tried the BIOS fix but it did not work, and that you are aware that the only available fix is to change the motherboard......
More info here : http://h30434.www3.hp.com/psg/board/message?board.id=Internet&message.id=1354