Why tv won't turn on and has 8 blinking lights on a panasonic tc-p50ut50?

Check and replace damaged component/s at its back-light inverter board, or replace this board as card basis. If you wish to get some details; check the site linked here. Surf the site with patience. Pull up older posts. It will be best to replace the inverter board as card basis.
http://electronicshelponline.blogspot.com/
To some model sets; especially LED back-lighted types; the back-light inverter circuit will be part of the main power supply board [SMPS]. In such cases, the power supply board might need replacement.

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given. Surf the site with patience.
Type in the brand name and type of your device, in the search box [at the top right] of the display window. It will make surf easy.

Look in the circuit board area where the power cord mates with it for capacitors that have bulging tops (instead of the flat tops that are normal). If you see even one, you need to replace all the large capacitors othe power supply section (normally around 5 or 6).

These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. http://electronicshelponline.blogspot.com/
Blinking codes details to many popular brand TVs are given. Surf the site with patience.

If you wish to get some details, check the site linked here. Pull up older posts. Check the site in 'Mosaic' view. It will make search easy. http://electronicshelponline.blogspot.com/. Blinking codes and troubleshooting procedure to Panasonic Plasma TVs, are given.

Try disconnecting all HDMI cables and plugging the TV into a new wall outlet. If the issue is resolved, it may have been caused by a small power surge from either your wall outlet or one of your source devices.

One the circuits popped. you can locate the bad board and replace. Use these charts to help locate the problem.

the number of blinks will determine problem area.