Inside the receiver seat belt is a sensor that recognizes the male end of the other belt and shuts off when buckled. More then likely the sensor has gotten dirty or the wire connection at the base of the belt has been broken or such. If the receiver end has gone bad, the belt needs to be replaced.
Thank you....I will check the sensor. There is nothing in the passenger seat.
In response to the other two answers...don't know why it came up that I live in Kansas...I live in Florida. Hope that answers your questions.