Why do my little pumpkins keep dieing?

I've seen about a dozen female flowers now on my pumpkins plants. They get about the size of a quarter than turn yellow, brown and die. I tried pollinating a few of them myself, but with no success still. I thought the cool abnormally cold June we had was killing them, but now it is July and temperatures are consistently in the 70s and 80s during the day. The soil around the pumpkins dries up more quickly than the rest of my garden. I generally water them about 5 times a week. Why can't the plants produce any good pumpkins?