Hey, I don't know if this will work on a Mac as I don't have one and I think they're a pile of crap.
But with a PC OS (operating System) there is a way.
When you logon you will have what is called a BIOS.
It will on a pc chekc all your hard drives,memory units etc.
It will also display at the bottom commonly 2 or 3 buttons to press for other options.
On most computers if you press F11 at this point it will take you into the BIOS but soemtimes they are pasword protetced if so Google the BIOS password for your computers make as they are on the web as Common Knowledge however if someone set up the computer for you, you may have to try "Password" "Pa$$word" or "Pa//word"
Once you have done this there should be an option to change the master password and this is how you can reset t.
Or alternitivaly if your computer is also malfunctioning.
Back-up your data to a Removeable Hard Drive and then there is an option to reset everything.
Hope this helps
Hex