bios password

hi guy ive gat a big problem i realy need help on this one ive have an acer aspire 3683 and i cant access anyting its telling me invalid password i need password to boot into windows and bios. i had a password set so i went to change so it ask me for old password entered it when it ask for new password in leave it blank and press enter and do it again to confirme it then i restart it.now when i leav password blank and prees enter it says invalid pass plz help