From my understanding, most DV6000s had a major hardware issue where the motherboard failed, whether or not that may still happen to your system, you might want to look into a newer system instead of dumping money into that one for that reason. However, what is the exact model of your laptop? Knowing that will give me a better answer. (it should be somewhere on the bottom, if it's not on the top, something like dv6292 etc.)
I think it would be money well spent to get a new laptop rather than try to repair & upgrade the old one. 1. You get all new hardware. 2. You get the latest version of Windows. The hardware you get will be of higher performance (for the same price) than the old laptop.