Ok, I find it strange that FIRST your channels were changing by itself (bad channel up or down button on TV or bad micro?) THEN after doing a Shipping Condition reset, that you could not lock in any of your TV channels at all. Could you SEE a picture at that time??
I know what we need to fix your TV, but I'm always concerned about WHY it failed. My first thought was "bad power" like a lightning storm or power line got damaged somehow. Or maybe a software update that went bad because it was connected wirelessly These are things I would want to prevent before allow the TV to be repaired. Keep those questions in your mind. If you have an answer that matches your situation, inform me.
Next, you need to KNOW which boards I suspect, and do some information retrieval so we can figure out which board or boards have lost your DVB-T channels. I've used colors to Highlight the board's locations inside your TV, and the screws you'll need to remove...not now, but eventually.
Lastly, I've highlighted the boards, and also the power line to your DVB-T tuner (we need to make sure it's powered up) and we also need to see if the VIDEO connectors are shipping picture and sound, and you can switch between them. Those tests will help us isolate the problem.
Also, if you check your various inputs on your TV set, try to check the Non Digital Tuner too. You have both, but the Analog tuner was the one that got shut off last year. It should only show black and white speckles on the TV screen (snow) but it actually is a VALID SIGNAL. Check that, check your Scart connections if you have Scart available on DVD units/games/recorders that you can play back on. See picture --