Sharp 60 in LCD-Model LC-60C6400U. Tv won’t power on. Has black screen. Flashlight test shows black screen. Reset did not work. One short flash and 1 long flash error light blink. I replaced the power board because I saw a cracked, capacitor and board looked discolored from maybe overheat. That didn't fix it. After reset the error light turns off now and stay steady lit. I hear it try to power on for split sec and see LEDs light up from behind panel but blink for a sec then Go back off. This repeats every 15-20 sec. any suggestions of what I should replace next?

copy and paste
https://www.justanswer.com/tv-repair/9gb1o-sharp-lc-60le810un-won-t-power-on-front-led-blinks-one-short.html

You have some bad lamps in the panel and its shutting down the power supply for the LED section

Hello... It sounds like you have a backlight failure, and the image going away during the flashlight test is due to the TV going into "Protection" mode. A service technician may be able to go into the service menu and clear the lamp error codes and get the TV working, or it may need the backlights replaced. I hope this helps...

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://electronicshelponline.blogspot.com/
In most cases, the main board might have to be replaced. If so, a software [firmware] update too might be necessary.

Not sure if you saw Tom's Guide
at Sharp lcd tv power button flashing

(1) 4tinyhearts said:
I unplugged the TV and held the buttons down and it continued to flash. I continued to hold down the two buttons and replugged it in again and it worked. TV back up and working.

(2) lastditcheffort said:
Unplugged it. After looking for a new tv online I decided to try getting it to work. So, plugged it back in and held down the power button, a red light came on, held down the power button again and an orange light came on, held down power button again and green light came on and tv powered on. This was simply a case of trial and success!

(3) Nateinportland said :
unplug, hold power button, plug in. If that doesn't work, unplug all the HDMI cables, unplug the power, hold power button, plug back in.

This is the board that has the bad part. http://www.shopjimmy.com/sharp-runtka932wjqz-power-supply-led-board.htm

Compare yours with the picture to see if there is anything visually wrong.

Sharp TV - Flashing OPC & Power Lights - YouTube

? 0:50
https://www.youtube.com/watch?v=BH1OcQ6dIEE
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Do a flashlight test. With the TV on and a program is playing, shine a flashlight on the screen. Can you see movement in the picture? If yes then the backlight drivers are not working. If NOT, then the T-con board is bad You can get parts from here : TV Parts Universal TV Stands DLP Chips ShopJimmy

How to perform a cold hard rest on the Sharp LC-60LE810UN TV? It won't power on and just blinks.

Sounds like a backlight either power to the backlight or the backlight itself. It's probably going to require a trip to a repair shop.