You have 2 main boards in a modern TV the power supply board and the T-con board.
It sounds like the Power supply board is working that is if the power is actually staying on. So this leads us to the T-con. What I suggest first is go to the TV and use the flashlight on your phone and shine at the screen where you would expect to see a video (I.e. the top corner where the channel box would be, or wherever you remember the volume display popping up) or if you actually hear a show playing just look at the center of the screen.. what you are looking for is an actual image playing on the screen, try from multiple angles and light distances until you are certain you either have or don't have an image...
If you DO NOT have an image on the screen then it's likely the T-con board that has gone bad, search your make and model on eBay the board is pretty inexpensive and pretty plug and play (BEWARE OF RESIDUAL POWER IN THE POWER SUPPLY BOARD!!!!)
this is the cheap and easy way to "fix" the T-con board but if you are more tech savvy then you can actually find out what has caused your T-con board to go bad.. likely a small capacitor gone bad but you gotta know what and how to test for them using a multimeter.
If you DO see an image on the screen using a flashlight.. you have a bad LCD/LED driver.. some/most drivers are built into the T-con board so you can just follow the same advice for if you have no image by replacing or repairing the T-con board.. some do have separate driver boards though so if you see a smaller 3rd board google the part numbers and this may be your led/lcd driver board..
Also, it's more rare and likely they all didn't go bad at once (but I have seen it) the LED strips that go behind the screen go bad.. typically there are 3 or 4 of these strips but normally only 1 or 2 goes out and you notice for awhile the screen is much dimmer in the top, center, or bottom..
Hope this helps, I started saving TVs out of the garbage this way and by no means an expert it was just a hobby and so I have no incentive to make a free TV work so there may be more proper ways of doing what I suggest here.. hopefully you get it figured out! Follow up with me if you do!