Q.Weeping cherry blossom blight?
White blossoms fallen off on the back half of the tree. They look dried up, crumbly, brown. Front is good
Certified GKH Gardening Expert
Without totally compromising the integrity of the tree, you should try to cut back any dead branches and clean all around the trunk of the tree. Have you examined the tree for borer insects or other signs of disease? If it's getting enough water and it not very old, you may want to take a branch to your local extension service or nursery for advice. Here's an article that will help you understand the ideal growing conditions: