Red light comes on but the unit wount turn on

The red light is associated with the memory (constant 12 volt power). You also need switched 12 volt power (power with key turned to accessory)for the unit to turn on. If you installed the system yourself, you are looking for 12 volts on the red wire of the Jensen unit. If power exists at the unit, check the fuse of the unit and the fuse of the vehcile.