Fault at its main digital board. Short circuited component/s at it. Contact any service technician; or the authorized service center.If you wish to get some details; check the site linked here.Surf the site with patience.Pull up older posts.
http://electronicshelponline.blogspot.com/
In most cases, the main board might have to be replaced.If so, a software [firmware] update too might be necessary.
Before going further; try a hard reset first.If it does not help you, replace the main digital board.There are two methods to reset TVs.The first is simple to do; a Hard Reset.The other is somewhat skilled; is a Factory Reset (System Reset). To make it a hard reset, just unplug the TV from AC mains wall socket, and re-plug it back after 15 minutes or so. If you do this by overnight is better. This procedure will make it a hard reset.If you want to make it a system reset [Factory Reset]; you have to enter its service mode option, and select the factory reset option.If you wish to get some details; visit the site linked here.