Calculating a sum with incomplete cell values

I am trying to build a worksheet for Profit and loss on stocks. The data contains sold stocks, and stocks still open. On the stocks that are still open I have the ifs function in place so the p/l wont calculate till all the data is entered. My issue is I am trying calculate a total p/l for all sold stocks. When I put the sum function in to calculate, I keep getting the #N/A in the p/l total cell. Is there a way to calculate the sum for the cells that have all the info entered and omit the cells that are not completed? I am sure its an easy fix but I am fairly new to Excel and have been trying anything I can to get it to work and have had no luck yet.