TV has sound but picture disappears after about 30 seconds.

TV has sound but picture disappears after about 30 seconds.

The tv that I have is an LG 42LB5600-UZ, but that wasn’t one of the choices. The problem is that the television turns on… has a picture and sound, and then in about 30 seconds, the screen goes black but the sound continues. It is the same on every channel. It worked fine last night, but not today.

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