Thin horizontal line across the entire TV screen

Question

Hi,

Our TV has a thin horizontal line across the entire TV screen. I know that the picture has collapsed (Vertical?). We used to be able to hit the TV a couple of times and the picture would come back. Well it won't anymore. Sice it seemed to be an intermintent problem, I figured there was a bad solder joint somewhere on the board. Can you point me in the right direction? Where should I be looking? Any help would be greatly appriciated.