Is it an automatic? If so, check that the button on the shift stick pops out. If it is still depressed / stuck then the steering wheel and ignition will not engage.

My S40 problem is intermittant. Sometimes when I park I cannot release the key from the ignition. I have had to start it up again, drive it around for a while and try to park again and that has released it so far. I have changed the battery, that didn't help. I have figured out that it is due to the...