Hi
Mary has had this again and I've figured out that the computer isn't really locked, it's a full screen page that emulates your browser Window. Nothing works because it's only an image of the screen. The buttons aren't real but you think that your computer is locked up.
What it is doing it trying to get you to do is call the phone number on the screen to get support, I'm sure that if you do, they will offer to fix your computer for a fee.
All you need to do is close the browser.
I ran a scan afterwards and found nothing.
Mike