Front windshild wiper is not working but back ones are. what is my problem?

The fuse could be blown, or the motor could be bad, or the switch may be bad, or the wiring in between.

CHECK WIPER AND FUSE AND RELAY.IF ALL IS GOOD CHECK FOR POWER TO WIPER MOTOR.IF YES.REMOVE WIPER HOTWIRE IF WIPER MOTOR WORKS.YOU HAVE BAD GROUND OR BINDING DAMAGE LINKAGE.IF WIPER MOTOR DONT WORK WHEN HOTWIRED WIPER DONT WORK REPLACE IT.IF NO POWER GOING TO WIPER MOTOR.CHECK FOR POWER AT WIPER MOTOR SWITCH.IF YES.SWITCH IS BAD OR HAS A BROKE WIRE.