Stuck on password screen

I have a Toshiba Satelite A350 which on startup gives the Toshiba logo screen, then goes straight to a black screen with a blue box requesting a password, which it has never done before. It will not accept my administrator password.
I've tried pressing / holding F8, but this only delays the password screen appearing till the button is released.
Vista Home Premium came ready loaded with the machine so don't have a disc to reload this.
Any ideas?

UPDATE! I have tried the continually pressing of F8, but was still getting the password screen.
Have now tried the bios wipe jumper that Patonb suggests on my previous post for this, but now all I get is a blank screen with no cursor. The system seems to be trying to do something, ie. it doesn't go into sleep / powersave, but I gave up waiting after 2 hours.
HELP!

Hello. see if you can do this procedure. It will allow us to do 2 things. kinda checks status of hard drive and allow user to save all their data . Use Ubuntu Live CD to Backup Files from Your Dead Windows Computer - How-To Geek Post back if you can do this please.