My Macpro will not sign in?
Resetting User Password in Lion and Mountain Lion
Boot into your Recovery Partition by holding down the Command and R keys whilst booting.
When the Recovery screen appears, go to the Utilities menu and open Terminal.
In Terminal, type:
...a small app will open and allow you to choose the user for whom you want to change the password. If you are the admin, be certain that you choose your admin user. Type in your new password twice and give yourself a good hint. Click OK (or Done or whatever) and reboot, enjoying the use of your new, hopefully memorable, password.