Try holding down the power Button until it shuts down, then try restarting. If it doesn't work, while on your home screen (after you're logged on and it's turned on, right click and press refresh. If it still doesnt work, If your computer is a laptop, then take the battery off and let it sit for a while, then try this process again. It might take a few or many times, I went through this process many times with my windows 7, it eventually worked.
Hope it works :)