Hello and sorry you're having problems.
We often see these sets develop faults after a few years, and in most cases it requires replacement of a component- specifically the Mainboard- which is what selects and processes the AV/TV Inputs.
However it's worth it to try a hard reset, as sometimes the processor in the TV can simply have locked up.
The first thing you would try, is disconnect the set from power, then press and hold the power button on the TV itself (not the remote), for 10 seconds and release. Then plug the set back in, and also check that the power cord is connected tight at the TV as well. Power the set up and see if you can switch Inputs on the set.
If not, then the Mainboard which processes all of the audio and video signals has a bad EEPROM (processor) and needs to be replaced. If you have this done at a shop, it's typically in the $200-$250 range depending on model, and is usually more cost effective to replace the TV.
Alternatively if you're looking to repair this yourself then I would need the model number off the back of the TV and I will dig for a source for the board.
If you need further assistance let me know. Please do not forget to click a POSITIVE RATING before you go- as it's how I am credited for my work. You can follow up at any time, at no additional cost.