That sounds really scary (as in bad news). Shut down the computer, then press f8 a lot until you get a menu for safe mode. See if you can do anything there.
If it's new or has a warranty take it to where you bought it and they'll fix it or replace it. If you've had it for a while then they might not help you and you might have to re load the OS (which is like a hundred something dollars).
Also try scanning it with a anti-virus (but use a different computer and connect them via usb). Maybe it's just a virus that is sending you the message about windows not working.