Admin Password is wrong

So I have had 2 of the same MacBooks. The first one I had no problems, but my current one has a lot of problems. The main one is the admin password not working. When I try to type it to unlock security preferences, it says it's wrong. I'm sure its right because I can log in fine with that password, and the admin password works in other preferences. I really need to update some settings but it just doesn't work.