A live CD (Non-Windows) should let you deal with it. I personally just slave the drive.....no boot, no game?

Otherwise you might try going into BIOS and Windows and turning off all screensavers and power saving. Then try safe mode, or get into control panel real quick.

You didn't say what version of Windows......................?????, or if you have CD/DVD, USB, floppy.

A HijackThis log is frequently useful with these problems, as you don't say what the particular form of scareware is.

A method I have used is to just give it a fake plausible e-mail and password......... chances are they are so greedy they won't pass the opportunity because you are not on the internet?...........that might buy you the time.

Good luck!