Bios error? I cannot open windows except with a password?

I have a toshiba laptop that suddenly required a password when i opened it. it doesn't let me in. it just opens a black screen with a blue banner asking for a password, which i don't know what it is. some told me that this is a problem with the setup in the computer bios and that i need to find a function key to clear the bios entirely. how do i solve this??