TV seemed to be ok last night but today now the picture is darker

TV seemed to be ok last night but today now the picture is darker

I have a 2009 Sony 40" tv. It worked fine and then I went on vacation for a week (just got back last night). TV seemed to be ok last night but today now the picture is darker (so are my playbacks on the DVR). I've tried everything (increasing the brightness, etc) but it is still dark. Any idea what it might be?

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