drop my speaker and now it has no sound at all

Hi Ka Ming Chan,

I would suggest you to open up and check for any possible stuffs, like wire connection drop out, broken solder, etc . That would be a good start.

Cheers

Hi Ka Ming Chan, Augustine's suggestions are good. Dropping any electronics could easily break a connection or wire. Speakers work with a moving diaphragm called a cone. The bottom of the cone has a coil of wire around it with some thin wires connected to it. The coil of wire on the cone fits around a magnet but does not touch the magnet. Sound signals in the coil interact with the magnetic field from the magnet which causes the cone to move giving sound. The magnet is normally only glued in place and can dislodge and touch the cone to stop the cone moving and prevents sound. Open the speaker and look at the cone. Be careful not to crease or hole the cone. If the cone does not move freely then something is touching the cone. This is often the magnet has moved or mounts of the cone have bent or something. Try to reset whatever has moved or bent so that the cone moves freely. If it still does not work after that then there is something more seriously wrong.