What are your specs, this game is a processing whore.. takes like 1ghz process just to run THE GAME, then theres demanding levels, and backround apps
turn your postprocessing off (ingame options) also play it in windowed mode
before you click PLAY GAME, theres an option menu.. click it and lower graphics to low, and play with settings to lower quality to bear minimum and it MIGHT help you out, also you are running a game proccess booster? i read pandora, i use Game booster 3