Please HELP!!!!

Hi i have a 1974 plymouth duster. The windshield wipers have worked since the day i bought it. The other day it started to rain so i turned my wipers on the passenger side one went up and stopped the other one worked. I moved the pass. one down so it would stay out of the way and i could use just the drivers side and today now that one wont work. I can here the motor running how do i get them to run again is it a belt what
thanks for the help