You should be able to call the 1-800 Sharp customer service number and ask them that question. They should be able to tell you how to do it over the phone for free, regardless of whether you have a warranty or not.
I'm not sure about the Sharp, but on the Vizio I had the customer service person on the phone told me to unplug the TV from the wall, then press and hold the power button on the TV for 10 seconds. Then plug it back in the wall.
Did you at least try unpluging it from the wall, wait for a minute or two, then plug it back in again?