Needing to smack it SCREAMS cracked solder joint.
The ride home could have easily broken even a marginal joint loose.
I got a 10 dollar 27" Panasonic TV off Craigslist this way.
I love it when they say turns off randomly

.
My 13" test TV on my workbench had the same problem. After my hand hurt from being the Fonz I decided to find the little gremlin in that set too.
The only way to find them is with a magnifying glass and patience.