I have a Panasonic crt tv purchased in 1995. Today I was watching a Star Trek rerun when I got a black screen except for a horizontal white line in the center that lasted only a few seconds, then all was black. I tried the Bill Gates method - turned it off, counted to 10 and turned it back on. Still black screen, sound was ok. About 15 minutes later I turned it on again and the picture is back! What could this be?