Time limit does not lock PC for account

My daughters time limit is exceeded and for a short while it notified her and locked the account as it should. She kept logging back in to her account and eventually Norton gave in and stopped locking the account. When I check the remaining time on her account, it says that time is expired and if she continues to use the PC, her parents will be informed, which is pretty pointless in my opinion. I need the PC to lock and stay locked.