As Pommie said, I'd look for a cracked solder joint somewhere, especially any solder joint that is large or thick. You can come across micro-cracks that you cannot see with the naked eye, and may even be hard to find under a strong lens. Do some solder iron testing by heating any larger joints. Avoid the really fine joints unless you have an adequate tip on your iron for the joint size. Look it over carefully under a high-power lens and a bright light. If dropping it caused the failure, I'd bet on a mechanical break somewhere...