Please try this:
-disconnect all audio/video wires from the tv.
-unplug the tv POWER cord from the wall outlet.
-press and hold the power button on the tv for 20 seconds and release.
-plug in only the tv power cord and try to turn on.
If that does not help then unfortunately there is not going to be any easy reset/fix. The Tv has an internal failure and the back panel needs to come off, checks need to be performed, then parts ordered and installed. If that is something you want to attempt then reply back here and I can assist you further (prior electronics experience is needed).
If you are unable or unwilling to perform any of these procedures then a repair shop should be consulted. A shop charges $125 to come diagnose the problem and hand you an estimate. Then another $175 in parts and labor. So the total can be $300 (or more).
I'm sorry for the bad news. Remember that I am here to help you. Please reply back if you need clarification on any of the above.
Regardless of what you decide to do next, please take a moment to click the 3 to 5 STARS rating at the top of the page. Keep in mind that I have donated my invaluable time and expertise helping you rather than other customers. My livelihood truly does depend on your positive rating.
Rating now does NOT close the question or prevent us from continuing our conversation here and selecting the "bad/poor" rating does NOT do anything to fix your issue (nor does it issue you a refund).