I think you may have killed your gpu by putting it at max settings, with lower end/not as capable or older systems I always recommend starting at low game settings/recommended game settings then ramping up the game quality to a safe place.
It may also be your ram, however. I put in an extra 8GBs to my other computer system and it would cause any game to freeze for a while or just crash completely. If you have added ram, or have old ram that may need replacing, replace it or take out the new ram you've put in.