Why Can't I Turn The Key In The Ignition Of My Classic Saab 900?

Probably because your car's belly button is in desperate need of a clean, you minger. Because the ignition is on the floor between the two front seats, it acts as a sump that accumulates all manner of dust, fluff and other everyday debris. People with young children will nod knowingly at this point. Spilt fruit juice or fizzy drinks are particularly good at gumming up the works.

Eventually, depending on how manky the owner is, the ignition barrel clogs up and the key won't move. The short term quick fix is to spray a little WD40 or similar releasing fluid directly into the ignition barrel and gently work the key back and forth until it frees up.

In the long run, you will need to do a proper cleaning job down there by unscrewing the face plate and removing the green ring (belly button ring?) to get right into the barrel and remove all the gung you can find. Methalyted spirits and a good quality cotton bud are ideal for this job.