If you are talking about the round kind with the slats in the sides, the probale reason they will not spin is because the bushings in the top have run out of lube. try taking a can of wd-40 {or similar product} with the spray tube attached, stick it in the vanes and try to get it to spray on the pivot point in the top inside of the vent. spray away my friend,all you can do is help. its that or have a roofer come out and replave the vents with a ridge vent, which is better anyway!
