Take it to a repair place or review your receipt and see if you bought the extra warranty but it sounds like its on its way out either way. Check the model number online for recalls.
Did this just start or has it been this way for a while ? Do you have a surge protector on the cable line as well as the power ?
I have a 27" Toshiba, regular type TV (not plasma or flat). After 3 years, it now flashes slightly brighter and has no audio from TV speakers and no closed captions. Then, it shuts itself off after about 15 min. when tuned to a cable channel.
If I tune it first to Video 1-3, or Color Stream it will not shut off. But it seems to need to warm up before the sound and captions will come on and then everything seems fine.
Have I done something wrong? Is the TV on the way to the junk heap?

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