Do the fans humm when you turn them on? They could be corroded and the motor shaft has seized. Or, the switches are bad, or someone disconnected them. Checking out the switches is fairly easy if you have a test light or a multimeter.
You should have power on one side of the switch, and when you turn it on, you should have power on the other side. You might need to go into the attic to check for power at the fan itself. Sometimes you can access the connections from below, sometimes you can't.