No picture and no sound. blue light in front flashes

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://electro-medical.blogspot.com/
http://electronicshelponline.blogspot.com/
If blinks continue without any pause, the main board is faulty.

If you have power to the standby light but no life beyond that you could be looking at a main tuner pcb: Link attached:

Search results for LC 50LE751K

Hello,

When your television actually flashes the front blue light, it is passing a message that there is a problem inside the unit. There are 2 things you should check but my best bet is that it is the t-con board of the television that is bad. The other component you can check is the lamp, but if the lamp is faulty you will not be getting sound therefore the problem is from the t-con board.

It is located by the middle of the main panel of the television, once you get it replaced, the television will be in good shape.

Take care and good luck

Most likely the lamp is dying. Try replacing the lamp before calling a repair tech. What does the Owners manual say about the blink lights?

Hi my name is Eric,
I hope I can help you with your issue ,
Sounds like a bad lamp assembly , search for one online by model# for between $100-$200
easy to install yourself
　
　
　
　
Hope this helps, if it has solved your issue please click accept
But if you have more questions please respond and I will reply asap
Thanks
Eric

I’m happy to help further over the phone at https://www.6ya.com/expert/eric_ab7c09ec01841771

no picture and no sound blue and red light flashing continually cannot turn off unless we unplug it.

The flashing light is giving you an error code as there has been some sort of failure in the TV. The buzzing sound could be the flyback transformer. Count the number of flashes. I'm sure the code will be for the flyback.

no picture

post your model. Sounds like the blue CRT is shorted. But let me know the model and I will let you know how to test it.