System startup disabled

Hello,

I recently went to start up my Compaq Presario v2000 notebook and when I turned it on, it made a loud, short beeping sound and the screen went black. A blue window popped up asking for an 8-digit password, the entered characters filling up a blue bar (that looks like a loading bar) instead of individual typed characters. I do not have any passwords, and have tried everything I can think of. After three entered passwords have been marked incorrect, a new box pops up saying "System Disabled [13504]" and nothing else. I have AVG and do not know if it is a virus or not, but am hoping it is not. I have had my computer for two years now and have never had any viruses and have never seen this happen before. If you know what it is and how to get past it, please help.