When ever I start the game up it is usually fine, sometimes the black monitor problem attacks then, but when ever I am playing the game I get like 5 minutes in and then my monitor will go black for a random amount of time and when it comes back on, it will go black again. It keeps at this until I Alt-Tab and close Portal 2. Once I close the game, my monitor will keep having the problem for 1-4 minutes and then the problem is gone until I play Portal 2 again. I have checked my GPU temps and power consumption during the problem, and the temps never go over 40 degrees celsius while only consuming about 30-50% power. This is the normal for most of the games I play. GTA 5 consumes more power and is usually around 60-70 degrees celsius and the problem never occurs. Can someone tell me what is wrong?