Before you take your vehicle to a car audio specialist, you might want to try fixing the problems yourself. There are some small adjustments and repairs you can make that may drastically improve your radio's functionality and reception. By checking and tweaking these things, you may find that your radio works quite well.
A radio that does not work at all may be a dead radio. It may also be attributed to dead fuses. Find the fuse box in the dash of your vehicle. Open it and locate the fuse that controls the functions of your radio/CD player and/or MP3 or WiFi connections. You may need to use your owner's manual to find the correct fuse locations in the fuse box. Pull these fuses out and replace them with fresh fuses. (Fresh fuses can be purchased from an auto parts store.) Now test your radio. If it still does not light up or read a digital time, you may need to check the wiring.
The Electrical Wiring
Uninstall the radio deck from your dash. Carefully pull it out of the dash. Examine the wires that should be connected to the back of the radio. If any are loose, reattach them, but make sure you are reattaching them to the right ports or contacts. If any of the wires appear damaged, as is often the case when rodents get into the engine of the vehicle and chew wires, you will need to replace the wires. Now, with the wires fixed and/or replaced, and the fuses replaced, you should get some sort of sign that the radio is working. If not, there is one more thing you can check.
The Onboard Computer
Currently, all cars made after 1990 have an onboard computer. This computer is a box about half the size of a car battery, located near the engine block. If you find it, open it up. There are several ports in it that are labeled, which tell you exactly which port controls what part of the vehicle. Find the one that either says "audio" or "dash functions." You will need to have car computer tester on hand, but then you can test this port to see if there are any electric signals exiting it. If not, the problem with your car's audio is in the onboard computer. A professional mechanic will need to crack that open and fix it for you, but at least you will know exactly what the problem is before you take it into the shop.