Look at the flowers. Pumpkins have both male and female flowers on the same plant. THe male flowers open for 1 day, then die. Those are probably the ones you are seeing. They are usually the first to show up. Then come the females (they have a bulg below the bud). When the males open (in the morning) you or another pollinater, must gather the pollin. Then when the female flowers open, the pollinater brings the pollin back and deposits it into the female flower.

Here is a link that might be useful: Pumpkin pollination

If you are in a situation where you need to pot it, is it possible that there aren't any insects around to pollinate? I'm in a situation like that so I do it by hand.