I forgot my pword on my computer!?

On my other laptop (this is my mom's almost 10 year old one) I changed my pword because my sister snuck onto mine at dusk, and I changed the pword. The next day (today) I tried logging in to it, bu I guess I put a typo in the pword, so I can't log into my computer! I tried F5, but that just makes the page brighter, so I tried F8, and it made the volume lower! HEEEEELPPP! MY COMPUTER IS MY LIFE!