If this is a password in the BIOS or elsewhere (not just Windows login password) you may have to call Acer and be prepared to produce evidence of purchase or legitimate ownership.
Advice to all: if you're the kind of person who can't be fagged to write down passwords in a book and keep it somewhere safe, don't put a password on your computer. These days laptops employ fairly serious digital protection against theft but it's not much use if it only serves to lock you out.