that happens for child lock or opening needs password, which you should have before blocking.
go to menu if you are over 18, look for settings, child lock, and unlock - needs password to unlock - read manual for default password
if not reset the whole receiver to factory default, and retune a fresh.
before resetting you must know how to set and tune a receiver, otherwise you could loose even the other channels open.
if blocked by your elders, parents etc, then ask them to open, cause they have a reason to block