Hello and welcome to justanswer.com
You should first check the fuses for the amp and radio. The fuses are #9 (10 amp) in the driver side heelboard fuse box and fuse #12 (5 amp) in the passenger heelboard fuse box. The heelboard boxes are located in between the rear seat bottom cushion and the floor. The carpet cover needs to be poped off and you will see the fuses boxes on the driver and passenegr sides. You also need to check fuse #12 (30 amp) in the trunk fuse box.
If you have premium sound then all the speakers are powered by the amplifier. Check to make sure the amp is connected. It's located above the cd changer. If you do not have an amp then I suspect a problem with the radio.
The amp is on that stack with the CD and the NAV module in the left side of the trunk. You will need to remove that side carpet cover and you will see the amp. Make sure that the two white connectors, the black connector and the data cable is connected. Then go to the 12 pin white connector and check for power at the brown/red wires (pins 3 and 9) and check for ground at the black wires (pins 2, 8, 11, and 12). You may have to remove the amp from the stack to do this. The fuse for the amp is fuse #12 (30 amp) in the trunk.