Smacking it is a way to diagnose the problem. If the red comes back or flickers when you smack it then there's almost a 100% chance you have a dry joint. Then it's time to go looking for any suspicious joints and resoldering them.
Dry joints look something like this:
If you've never done any electronic soldering before it is a good idea to practice on a scrap board first to get a feel for it.
If you've never done any electronic work at all it may be a better idea to get someone else to do it for you. The high voltages present in a TV can kill you if you touch the wrong thing and some parts will retain a charge even when the set is off and unplugged.