It could be a number of things... knowing the type of TV you have, plus the make and model would also help. ;-) In the mean time, if its a Samsung LCD, there is a known issue with capacitors failing after a few years. It won't turn on, but it'll make a clicking sound. You can read about how to fix the problem on this webpage... thankfully the fix is fast and cheap.
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You might try resetting the tv. Look in the manual for how to do that. Fixed mine that way once but with a different problem.
probably bad capacitors.If you don't know what that means, then you should probably have a qualified repair tech look at your tv, or send it in to retailer/manufacturer for warranty repair.If you know what that means - then you know with a soldering iron and some online ordering you can get replacement parts for just a few bucks.http://www.youtube.com/watch?v=72sJ5Infuu0http://www.youtube.com/watch?v=Ytw57212X2o
i love capacitors