30 minute countdown?

My mate recently fit a cd player in to my car when we giit it wired up n fit in. It asked me to enter the keycode in..which I did vut then after I did it had a 30 minute countdown on it..after waiting 30 minutes I entered it again and it worked..after being on for acouple of minutes it froze so I turned it off n it said enter the keycode again and had another countdown of 30 minutes could you please tell me why n how to solve this problem please!!!!