I get the same message on mine whenever I switch from any input to the one with my cable box. It's only for a second or two, then the picture comes up. I switche the box to another input and the problem followed. That proved it was the cable box. Try doing that and see what happens.
Keep getting message stating weak or no signal. Seems to do it after tv has been on awhile. I have a DISH DVR receiver. The second tv on this receiver continues to work fine. The Samsung is only 6 months old. I'm trying to determine if this is a satellite or tv issue before going any farther. Any ideas?