The problem is an issue with calcium absorption which is sometimes caused by irregular watering.
Add calcium to the soil with produces like bonemeal or install a drip irrigation line so plants can drink water slow and steady.
Flowers but no fruit
If you are getting lots of flowers but no fruit, it could be because your plant is too young.
Zucchini plants produce male flowers about 8 weeks before the female flowers develop. Then they will produce male and female flowers simultaneously for the rest of the summer.
Male flowers have long and skinny stems. Female flowers are usually larger, closer to the stem, and have a small immature zucchini behind the bloom that looks like a thicker stem.
Sudden death
if your healthy plant suddenly starts to wilt and die, the problem is probably a bug called squash vine borer. These moths lay their eggs inside zucchini stems and the caterpillars eat their way through the plant.
Usually the plant will have damage close to the soil line that almost looks like rot.
The best treatment is prevention. Lay a mesh cloth over your plants in June. This is the month these moths are most active in our area.