Usually just hitting Enter at the BIOS password just causes is it use no password. If you changed the password of course it won't take the old one. Just hit Enter at the password and see what happens. You can also try to reset the BIOS, unplug the battery and wall power, open the laptop case, usually where the palm-rest or keyboard is, and unplug the BIOS/CMOS battery for a few seconds. Replace battery, power it up again.