I have a similar problem, but no manual either. I've heard some manufacturers "booby trap" their tvs. If they are tampered with, or are opened in any way (repairs) they become locked if a certain procedure is not followed. If you have the original owners manual, try contacting the manufacturer.
David
January 2008
I can answer this question...
forgot my unlock code for my tv and dont have original remote?
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Try fixfault.com to fix televisions.