Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts.
http://electro-medical.blogspot.com/http://electronicshelponline.blogspot.com/
In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.
Can you hear your neighbors banging on the wall to turn it down?
You may need to talk with an audiologist to get some answers regarding possible equipment that has the right frequencies and volume you need.
Verify that antenna connector conductors are properly isolated and properly connected with TV. It seems the antenna connector cable is either short or opened.
You have a board that has gone faulty, or perhaps failing capacitors. Take it for service or replace it with something better.
It appears to be made in China and not a brand I know here in Canada. Seems to ring a bell from when I lived in the UK.
https://www.google.com/search?q=Finlux+42FLHT911LH
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Capacitors can fail without any outwards signs of it. You need special equipment to test them unless you are willing to change all of them. It is not that expensive to do.
