reset my radio?

my6000CD Ford radio in my Cmax car will not let me put in the radio Code. the car battery has been disconnected a few times recently to allow various other items to be repaired. ie; Starter motor renewal. when reconnected the radio works without asking for the security code but it is difficult to reset the date and time. I can never reset the date and if it occasionally allows me to reset the clock it changes to some random time within a very short time.
Any help would be appreciated.