Starters sometimes develop a dead spot and is usually the first sign of a starter going bad or it could be a loose wire in the ignition or solenoid going bad. Go to a auto parts store like Advance or Discount and have them check out your starter for you, it is free and is the most likely suspect. If the starter is not the problem then take it to a dealer or a shop that specializes in Volvo's and has a good reputation, good luck.