Painting - using a paint sprayer

I was recently given a semi new paint sprayer. I have all the tools and attachments but no instructions. It looks simple enough so I attached the air line from the compressor to the painting gun which has a resivoir for about a quart of paint. I let it get up to speed (which took about 10 seconds) and pulled the trigger but no paint came out. I tried to thin the paint but to no avail. Air was coming out of the nozzle but no paint. Any ideas or suggestions? I am painting an outside deck with it---to paint it by brush/roller will take weeks.

:) have you checked to see what type of nosal it is?..sometimes in a new nosal there is a small peace of filler,so air might come out but no paint..check it out..