My TV has a single horizontal line in the middle of the screen.
Every time I vibrate the TV by tapping or walking it jumps to full screen and then back to the single line.....Sometimes it does this on it's own.

Kevin Bowers, January 2006

If your T.V. is the model I think it is you've got a bad soldered connection on one of the voltage regulators. These look like 3 legged power transistors and are mounted on an aluminium heat sink, carefully resoldering (be careful not to short the regulator out) of the legs should correct your problem.
Take care.

Dave., January 2006