I had a similar problem once and it turned out it was my graphics card. I ended up having to reball it. This is where you strip down the graphics card to just the board with the gpu on it and stick in the oven at like 400 degrees F to remelt the soldered connections under the gpu and elsewhere as they can crack from high heat, cycling or whatever, thus poorly conducting electricity. High temps from dirt or insufficient cooling from fans can cause such damage.
What does the word "reball" mean? Think of the solder in a molten liquid state being shaped like a ball. I am assuming manufacturers call them solder balls during manufacturing of the board.
When I put it back together and reinstalled it, it worked like a champ. It's a poor...