I'm sorry to hear that you're having this issue.
Unfortunately, I can't diagnose what's wrong with the unit. In some cases, it might be the electronics causing this, but to know for sure, it'd have to be inspected by a technician.
My samsung plasma model # PN50A450P1D suddenly got a black horizontal li ne running accross the screen yesterday. It appears on all modes, tv or all video games (ps3 and Wii). Is there any solution - my husband is about to have a heart attack over this!! Thank you !