Just got my welder and it wont feed wire all amps are right and everything is hooked up good. When i turn unit on it powers up fine but when ipull gun trigger wire feeder wont move, i can hear the gas valve open and close. I read other post on here and tried loosening the three screws but nothing. So i shook it and it worked once i turned it off and back on it quit working any help appreciated. sorry not much for typing