The computer detected a problem and shut the system down so the bag won't deploy in a crash. Find a mechanic with a scanner that can access that computer to read the stored diagnostic fault code(s). They will lead you to the circuit or system with the problem, not necessarily the defective part.
The most common cause is a broken clock spring. That's a wound-up ribbon cable in a plastic housing under he steering wheel. As it continues to break, the horn and cruise control may also stop working.