Had this happen with a DVD player once.
Im not sure if your TV might have the same issue, but upon opening up the DVD player i discovered that right next to the power plug inside the DVD was a
small fuse which had blown.
A trip to the hardware store to buy a replacement fuse of the same amperage fixed the problem.
it worked fine for several months then happened again. I can only assume the unit was defective, or perhaps received some sort of power surge.
My advice would be to call a repair man or take it to a shop.
if you dont want to spend the money on that, open the TV up and see where the power cord goes in and look for a fuse (it might have one like above that you can replace on your own for next to no $)