You could have either poor pollination or no female flowers. With squash, you have male flowers (which have a long, skinny stem behind them) and female flowers (which have a small squash behind them.
When you see them both open in the morning, take a male flower and gently smoosh it into the female one, being careful not to destroy the parts in the center of the flowers.
Of course, this only works if you have females to pollinate. If you don't, just give it time. In many instances, the plant will produce all males before the females.
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