Remove the cover of the TV and find the ribbon wire that supplies the LCD of your screen. Clean it with a contact cleaner for possible lose contact. Then try to turn on the TV. Most cases lost contact is the cause of that line. After checking for possible lose contact but the problem still appear, that is more likely the T-CON Board was partially defective. You can replace the t-con board whole assembly. That is available now in the market.
Check your power supply output with a volt meter. If the power supply works properly and the output voltage fits to your unit requirement, then your unit may have problem. Just send it to the service center of that unit.
Try to replace with a new front camera. Maybe the camera was damaged during the replacement of battery. Sometimes, it happens that the battery supply input was touched to the other part of your phone and it happens that it goes to your camera and damage it. I have tried it to my other costumer with same problem.
The battery connector was the with that problem. But it is not easy to replace the battery connector, since it was connected/attached to the mother board. You can replace the mother board assembly but quite expensive. It’s better to buy a new one than replacing the mother board. Since the price is almost the same with a new one.