Have all the cherries fallen off or just some?
How old is the tree? Has it ever had a crop before? Did it have a crop last year? If so, what's changed this year? Does it get at least 8 hours of sun every day? Does the tree look healthy otherwise? Are the leaves looking healthy? Any windstorms lately? Is it a really big crop? If the tree can't support the size of the crop it will drop the excess naturally.