Are you connecting your TV up using these cables ?
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If you are, I've seen the Red and Blue cables get pulled out of the TV or Cable/Sat box's sockets just enough to give you a Yellow and Blue picture, yet they still look connected to the socket. I always recommend pushing those plugs in and make sure they are fully seated, even if they do look like they are connected.
Reply back to me and let me know the results if that's the connectors you use to get your picture and sound from the cable/sat or DVD box.