I used to do this at my high school computers using Linux and the command prompt. I have also done this with my personal computers as well. I used a Linux operating system from my usb drive and ran it on the computer. I then changed the name of sticky keys to that of the command prompt so instead of pressing shift 5 times and getting the sticky key options, I got the command prompt. I would then restart the computer and press shift 5 times to pull up the command prompt before I logged in. This is because before you actually log in to any account, you are already logged into the admin account. So now I had a command prompt window with full admin privileges right in the log in page. From there I changed the admin password to one that I knew and closed the command prompt and logged into the computer admin account itself. From there you can have the admin login show up with your other profiles by going in the settings.