“Help my violin makes no sound” I have had a few people ring me with this dilemma, usually after buying a violin on line. Generally speaking with a wave of my magic hand I can make a violin work 😉
Whats this magic you ask, its a little piece of rosin that should be supplied with your instrument , it nees to be passed over you violin bow about 50 times up and down, this creates friction on the bow hair (sometimes its nylon though) and then it works, Therein you only need to put it on the bow maybe every second time you play.
FWIW all violin rosin it not created equal, it needs to have a slight stickiness to it to help the bow grip, some rosin with cheap violins come with a really hard rosin that doesn’t work to well. You can get the best out of it by scuffing it slightly with some sandpaper (or a nail emery board) to get rid of the initial shine.
Here is bow rosining in action, so your violin can make a sound. Of course there might be more complex reasons but this is the most likely.