Was the pump working fine before during the season? The only reason I mentioned the ball valve being shut was if you bought the boat recently and this is your first time going through it. If that's the case then it's possible the previous owner or dealership closed the valve for winterization (or whatever reason). If the ballast pump was working fine and all the sudden is not then it's likely not the ball valve as those are just simple "gates" to allow water in and out of the thru hull fitting when the ballast pump is running.