Television and Home Theater

No picture, has audio, With back off I can see the backlight are on, No menu or anything on the screen, Panel or main board?  How to tell, dont have any boards to try  

lg led tv model number 43uh651v has only power blink 3 times after no videoand no sound power supply is ok when i turn on the tv from standby i can access from control panel or remote control but after its red umber light blinks three times nothing comes/no video no audio / and to turn off i can access only from remote control i can't access from control panel.i got one bad backlight led however after i change it the problem is still the same. please tell me what i have going to check thank you so much...

Hi there. I am very frustrated in the fact that i tried numerous ways to reset my Panasonic Projection TV. I even tried calling Tech Support and to no prevail that didnt even work. The Model # PT-52LCX16 and it is over 10 years old. It is great condition. However I cant remember my password to unlock it. Please advise. thnks