Turn on the radio. If you hear static, the problem maybe in the antenna. Or the radio housing’s electric ground may have loosened. Connect a jumper wire (a length of wire with an alligator clip at each end) securely to body metal and to the radio housing. If the radio then plays normally, look for a grounding wire, usually black, leading from the radio housing to body metal or to a dashboard brace. Clean and tighten the connections at both ends or replace the wire if it is broken.
Other possibilities are a poor connection at a speaker or failure of a speaker. Most speakers are readily accessible under detachable panels at the dash or on the rear package shelf. Disconnect and inspect the speaker connections. If they are corroded, wire-brush and reattach them. If a spade-type connector is loose in its terminal, crimp the edges of the terminal with pliers to restore a tight fit.
The most accurate way to check a speaker is to plug a new one into the wiring and see if the radio plays normally. Or you can inspect a speaker for obvious physical deterioration. None?
Disconnect the speaker wires and connect an analog (needle and dial type) ohmmeter, set at a low-resistance scale, to the speaker terminals; you should hear a static like click if the speaker is good.
If you hear no static, check the fuse box for a blown fuse. If the radio fuse is good, look for a second fuse in the wire carrying current to the radio. If your car has such a fuse, you’ll find it in a round holder that you can take apart. Replace the fuse if it is bad. Clean and tighten the metal terminals on wires going to the radio.