I think you're using a laptop based off your cpu and gpu? This is going to seem super basic, but it's happened to me once before and took me an embarassingly long time to figure out. Has your power cord come loose a bit? If the cord isn't properly plugged in, laptops will usually force using the on-board graphics card rather than your discrete graphics card in order to conserve power, and that results in abysmal frame rates since the on-board graphics cards just aren't equipped to handle any sort of 3D gaming.