I have a lg 55"

You probly will not be able to fix it your self ?

sounds like a componant in the tv is over heating and then shutting down till it cools then back on... this may very based on the room temp... you could try to place a small room fan near the tv, blowing twords/ on the back of the tv.. see if this makes the tv stay on, if it dose, then a tech will have to open up the tv and find the over heating part and add a heat sink or replace the componant.

other wise,,,,,, a different thing would be that it could be the signal you are trying to watch is weak and not decoding... try to watch a dvd or another input device and see if the picture stays on.

If it dose, then look for problems with your cable or your tv antenna.

hope this helps!