I had the same problem. all the service reset would only make the display come on for a few second with no "k" on the screen - only the channel would show up. I purchased a complete set of board for the lcd on ebay, and started swapping them one by one. The inverter boards were the culpret. Tele working 100% since that board swap.
power inverter board is dead.
need a new one.
Try to read an advice from
Fault with main board. Damaged 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.
Call sharp back again and tell them you first want to register for aquos advantage program, which is free. By doing that your service will go much quicker with them. You then tell them that you want to get set up for service. They will have one of their authorized professionals come and fix your tv in a matter of days. If their tech cannot fix it, they will replace your tv free of charge as long as you are within your warranty.
THe problem is in the set top box. Or common called the tuner box. IT looses the 5 volts to the main display and thus the monitor will go into a shut down state. THESE boxes are factory repair only and must be sent off to repair.