It may just be a fuse. try and locate the fuse box in the car, normally underneath the dash, and locate the fuse for the horn, (should be illustrated on the fuse box cover), and check it, if blown just replace, as for the airbag/steering wheel dont try to pry open the cover of the steering wheel as it will definitly deploy the airbag and could cause serious injury.
Doggyboy2008, June 2008