front windshield wipers not working

I recently bought this car and the front wind shield wipers are not working at all, but the rear wiper and windshield spray are working. i tried to change the relays and fuses also replaced the front wiper motor and still nothing. please let me know what could it be. The windshield wipers suddenly stop working from time to time. They will be operating perfectly, then they will just stop. When I turn the engine off, remove the keys, then restart the car, they seem to work fine again. Any suggestions as to a cause/cure for this? This model has the "auto" feature on the wipers, but the wipers shut off in any mode, with the auto feature turned on or off.