Did a clean install and booted up the game and did the stress test and average around 17 to 18 fps according to the game and during in game average around.....1 to 2 fps don't know why the game is running low fps any fix?
Your hardware might not be properly supported in win 8.1, has this setup worked before? Maybe you're better off downgrading to win 7.
What are your temps like? If this system hasn't been deep cleaned in a while, the coolers might not be performing very well.