Marco- are the HPs dv6000 or dv9000? I recently ran across this with a dv6408. Hit the power button and it doesn't go to bios, just restarts. After an unpredictable number of attempts it starts but the wifi is dead. The nvidia chip has come loose from the board and the solder beads need to be reflowed or the board replaced. (I'm guessing you know all that already). There is info all over the net on how to fix it by removing the board and heat shielding everything but that chip. You heat the chip and it resolders itself. You can use anything from a really expensive looking machine to a heat lamp and tin foil.
Or you could do something profoundly stupid. Get the laptop to start (may take many tries) and go into the bios screen. Wrap the laptop in a blanket or towel, blocking all the vents, intakes and exhaust ports. Wait. It will overheat and shutoff. Start her up again and repeat. Repeat this as many times as you dare. When your nerves give out and she shuts down one last time, unwrap it and let it sit there, off, for an hour or more to cool down gradually. Test it out. Problem solved? Temporarily? Permanently?
I wouldn't do this unless you are ready to throw it in the trash rather than take the motherboard out. If you are crazy enough to abuse a laptop this way its probably a good idea to remove the battery and hard drive before you cook it.