Bit of a funny one...
Since XP works, I would look into upgrading the laptops bios... might help. - That is, if you are not already using the latest one.
See
: http://h20000.www2.hp.com/bizsupport...riesId=3466363 - for driver and bios updates.
You might have to temporarily install XP to do that which could take some time. As I said earlier, if it is still under warranty, contact HP support. You should be able to get a replacement system board out of them which doesn't have these problems.
I also found a troubleshooting page for the G6000 which may well be of some use, some of the problems here seem to match yours!
HP G6000 Notebook PC series- Troubleshoot a problem - HP Business Support Center