Do the headlamps or the accessories work? That would rule out a dead battery, if they work and keep working when you turn the key.
Last Saab I had was an '84 900. One day when I left work, there was no response from the car when I turned the key, but the radio worked just fine. I caught a ride home to get some tools and my voltmeter, but the car started up fine when I returned. Over the next two years I had two more such incidents that all fixed themselves before I could find the problem. Then one day I had one did not self repair. My mechanic found that one of the hundreds of connectors and/or relay contacts used in that model was intermittent.
-- Vic Roberts