i know what the administrator name is, but Mac doesnt accept it. what should i do??

All I can say is check to see if your caps lock key is on while you’re typing ( you’ll see an up arrow on the screen somewhere- could happen, maybe) maybe spelling?? I’m sure your spelling is OK. Otherwise reboot from the recovery partition, and in OS X tools go to terminal, and type in ‘resetpassword’ Then press the return key, this should get you to the reset admin password tool,and you can reset your password

John B

where are you being asked to enter the administrator name?