I'm sure you have already unplugged the tv power cord but please try at least one more time to be sure:
-disconnect all audio/video cables from tv.
-unplug the tv power cord from the wall.
-press and hold the power button on the tv for 20 seconds and release button.
-plug in the tv power cord only and try to power on.
If the problem continues 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 help you (you need a meter and some previous electronics experience). If you are unable or unwilling to perform these operations then a repair shop should be consulted.
I am here to help you. If you clarification on any of the above reply back.
In keeping with the concept of this site, please be sure to click the 5 STARS or SMILEYS rating now. Doing so does NOT close the question or prevent us from continuing our conversation here. My livelihood truly does depend on your positive rating.
I understand news of a failure is upsetting but clicking the "bad/poor" rating does NOT do anything to fix your issue, nor does it issue you a refund.