Last night my computer froze up completely, so I shut it down using the power button. Ever since then, every time I try to boot it, the screen saying "Windows did not shut down correctly..." comes up, with options to start in safe mode or normally. I've chosen all possible options, and it looks like the computer is starting to boot (it shows a screen with the Dell logo and a progress bar), but then it keeps going right back to that screen saying that windows didn't shut down correctly. I've tried shutting down the computer but it isn't working. What can I do?