ok bro this is what you do. 1. turn the comp off 2. keep tapping f8 until a new screen comes up 3. you will see a safe mode option. highlight it and press enter 4. there will be an account called Administrator 5. it wont have a pass 6. go to the control panel 7. change account. Actually, I tried this and the user account, Administrtor did have a password You can also create a new account:
1. At startup hold Command S
2. Type mount -uw
3. Type rm /var/db/.Applesetupdone
4. Type reboot
It will come up with the welcome stuff, fill out registration and your admin account will be created. You can change your old account from Limited to Admin, or keep the new one. Password protect the one and probably back up the user from Macintosh HD/Users/Your account to a USB so you can get it back if your evil sister changes it. Mine tried that too!