I have the exact same problem with my Samsung hi-def big screen and quite by accident found a way to “fix” the problem when I was plugging in a cable cord. After fiddling and wiggling the cable cord I eventually found the “sweet spot” and my picture returned to a beautiful screen display again! The only problem is if I accidentally turn off the tv I have to manipulate the cable cord again. It can take a bit, but eventually I find the sweet spot again. The odd thing is - the other end of the cable cord isn't attached to anything! Hope this works for you, too. Worth a try.