What is the make and model number of the TV?
Approximately how old is it?
Does the standby light come on?
Does it stay lit or does it blink?
Ok, it seems like the Input/Source button is sticking - either on the TV itself, or one the TV's remote control or another remote control that is programmed for it.
Can you try removing all remote controls from the room first?
If the problem persists, investigate the buttons on the TV to check if the Input/Source button is sticking down.
Let me know what you find...