The front panel has a blue light and power , but i am not getting a picture or sound.

If back-light is OK, the fault will be with its T'Con board. If you wish to get some details; check the site linked here. Pull up older posts.
http://electronicshelponline.blogspot.com/

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.

What have you got? The inverter, the mainboard?

It'll be one or the other...

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

The mainboard needs to be replaced

there are three commom problems with this set one is light engine color wheel or power supply to get any of those is hard they are in back order but on some cases if the power is bad this could be fix bad caps on it if you want to get deep on it e-mail me [email protected]

how do i fix p50h401 blue light no picture and sound

no kidding? what is the problem so prevelant in this unit? obvious design flaw.