2000 Ford Taurus Car cut off, won't start

For the past few weeks I've been having an issue with the car occassionally cutting off while ideling. Today while driving 55mph the airbag light came on and then the RPM guage and speedometer went crazy (up then down), my lights dimmed so I turned them off and the speedometer corrected itself. Great for 1 minute, then it all started again so I pulled over and turned off the car. Now it just clicks and won't turn over. Do you think its electrical, battery or starter or alternator