Certified GKH Gardening Expert
Male flowers, which are non-fruiting, commonly drop off the plant and this is common early on. Once the plant begins bearing female blossoms, it is normal for them to drop off as well when the fruit begins to form.
As for fruit shrivelling, it sounds like you may have a pollination problem. If you do not have pollinators, you will need to hand pollinate. You can do this with a small paintbrush. Just sweep the inside of the male blossoms with the brush to collect pollen and "paint" the pistle of the female blossoms. That should correct it.
These articles should also help: https://www.gardeningknowhow.com/edible/vegetables/squash/squash-fruit-falling-off-the-plant.htm