getting the average..

what formulas would i use to get and accurate average from a column? we will say row c20:c31. I would like to skip any value that is not greater then zero.

example, row displays: 25,125,0,0,0

I would like that range to show an average of 75... What i am getting is 30..

ps- the zero's will change later to actual values so i would like to formulas to count them if they change from 0 to a number.