Need to provide make and model of TV as they're not all the same. Common causes...
1) Faulty EAROM (memory IC) or loss of supply voltage to it.
2) Loss of tuning voltage. Usually 33V regulator.
3) On very old TV's faulty back-up Ni-Cad battery.
4) The TV is in Hotel mode and it needs to be deactivated.
5) Your TV needs you to press or select store on TV or in tuning menu to complete the tuning process.
Cobweb
October 2005