Sounds like you have a bad power supply issue, and costs for repairs, and parts can start amounting with time and labor. If you could narrow it down by testing the power supply yourself with a volts/oms meter you will be able to tell a tech. exatly what needs to be replaced., or do it yourself.

If the power supply is supplying the main board with the correct amount of volts, your controller board or your on off switch panel is malfunctioning and needs to be replaced. If its the whole board your looking at a few hundred unless you can find the same tv with a broken screen and just swap parts.
The on/off switch board is cheaper but you have to remove alot of interior parts to access and becomes a hastle.

I would attempt to diognose these parts starting with power supply and moving forward to narrow your search from most likely and cheapest to more expensive and harder. You can also do visual checking while looking through the tv to see if their is any burn damage from a short cuircut.

Un plugging and re-plugging in the tv multiple times will take its toll on the tv and start wearing out parts needed to function. This is what leads me to belive it was power supply that failed or the on off controler board.

Good luck

I would look on e-bay for a broken Tv identical to yours, with the screen busted out and just put your screen into it. Easy fix and its only a few wires to reconnect when you have them both stripped down, that and a few screws.

Take photos if you dicide to go that route and use them for a refrence when installing and transfering parts from 1 tv to another. Makes your job easier and nothing will go forgetten and un plugged