Ok, I think I know what might cause it. Its video chip that gets melted off the board because overheating. You can try to remelt it even without opening the laptop. Just turn it on and cover it really tight with sometihng so it gets overheated. Wait about 10 minutes and turn it off. Then uncover it adn let it cool and turin it on in 2 minutes and it is working. It´s just for fast access, it does not repair it for long term it only gives it better connection for a short period. To fix it you need some specialist you fix the issue, but it is most likely not worth it as pavilion dv6 is a fail in general and gets overheaten and that can cause other problems in future.
Also for heating you can use hair dryer. Check out videos in youtube what area to heat.
The heating worked fine for me for some time, but eventually I got bored and I just took the hard drive from that computer and use it as external.
What I did was removed the motherboard, took off all the parts from it that I could, including the plastic coverings, and baked it in the oven at 375 degrees for 7 and a half minutes. Put it back together and it booted. I don't know if this is easier than the other methods posted but doing it this way has worked for me on several laptops now and seems to last longer than heat gun method.