cold solder... cold solder... cold solder...
see if you can bang the krap out of it and make it work again..
if so you have a crackes(cold) solder jount..
9 out of 10 junk tvs like that just have bad solder...
check any and all transistors and ics that are heat sink mounted...
check around the power section, and also near the buttons..
i almost guarantee youll find it and fix it..