When you boot up keep tapping the (depending on setup) either the F5 or the F8 key, this should take you into Safe mode. From there run SIW.exe and look for passwords, and you should be able to see what it is.
The alternative is to look where the battery is located and you should see a 3 pin slot and a jumper with only 2 pins connected (Normally 1 & 2), by changing this to to 2 & 3, you clear the Bios and any passwords in the system.
The BIOS should reset itself to defaults but if it is corrupted you may need to install a new BIOS.
Leave about 5 seconds and change back.All passwords should now be clear.