cars?

hi, i have a 2000 nissan primera 2.0td, the airbag warning light is constantly on. i've been to three garages which tested the car with diognostic equipment. all three times there was no fault registered , i found a solution on another web site but this required the radio to be off while tring. for some reason my standard radio will not turn off with the ignition on. anyone come across this problem, thanks !