Try locking and unlocking your car 5 times. Then read this from Volvo Forum:

The main problem is the corroded starter wire that is starting the problem. When this problem starts you attempt to start the car and it "locks" or immobilizes the car from starting. So you have to do the lock/unlock 5 times as described above to reset the system. What I did was reset the immobilizer system and jiggled the set of wires going to the starter and it started. I have yet to undo the set of wires as they're hard to get to and I'm not a car person. Going to take to a friend and have him help. But if you're in a pinch and can locate where the start is, there is a set of wires to the left that you can jiggle. This allowed me to start it. Worst case scenario, take it to your mechanic and have them do this first before they start replacing crap.
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Keeping it running is better than buying new