Just put a new motherboard in a HISENSE 50 inch tv, it still has no picture. Only sound. I ordered a new motherboard and installed it a few days ago

dear it seems that the pcb got problem

Hi,
There is something wrong with its video section . Change video card I think it is faulty .

It all depends what has led up to the problem, however if there has
been no indication of something going wrong,ie. picture getting dimmer, the most common fix is to reset.
First just check all cables are firmly connected. If that does not work then....
Unplug tv, disconnect from cable box, satellite box, any receivers.
Also turn power off to them as well.
Connect everything back and turn on.

Here is a video of other generic problems that can go wrong on any
tv that leads to sound with no picture.
TV Has Sound But No Picture Troubleshooting Guide

If it is new I would definitely insist on having the matter investigated and repaired under warranty. It should not be doing that!

Go back to Walmart this must be a warranty issue.

http://www.manualwanted.com

If you still have back light, then the T-con is probably defective. If you don't have back light, then you either have a bad power board/inverter or a defective panel

any sound bar will work. i have a LG 50" with a Samsung sound bar with a optical audio wire going from my tv to the sound bar. it comes with a bluetooth sub woofer and it sounds great.

could be bad capacitors in power supply. 

sounds like the color wheel has gone bad..the part is not very expensive but it takes some work to replace it