Hello everyone

Being a new user not sure if im in the right area with my problem, but here goes.

Just recently bought a car with the avic-f900bt system and all ok for a few days but suddenly its asking for a password why i dont know the battery wasnt disconnected or anything i have entered tbe password i was given which the previous owner insists is correct and has used himself i have made 3 attempts still no joy. He did ask have i used the full stop and caps but the keypad has neither just 1 to 0 and a to z and space key dont know what to do now i dont want to lock it out

Any help would be appreciated

Regards chris