Why do my Squashes shrivel on the vine?
It's most likely to be poor pollination. Squash plants have male and female flowers. The female flowers are the ones with the tiny bulge behind them that then become the squashes.
If the pollinating insects are not doing their job then you can pollinate by hand. Just pick a male flower, take off the petals and rub the pollen from male anthers onto the female stigma. Here is a photo of someone pollinating by hand. http://www.smallkitchengarden.net/ycgt/wshandpollinating.jpg
Male flowers normally emerge before the female flowers.
Thanks for your interesting question.