bark falling off
Falling bark indicated dead wood underneath it. It it is on a branch, prune off the branch (do not leave a stub--do leave the branch "collar"). Dead wood on the trunk could be the result of winter damage, disease, isnects, or a lightning strike. Also, mechanical damage such as a car hitting the tree.
If a lot of bark is falling off, it suggests a lot of dead interior. Sounds like the tree may not survive.
For help deciding when to take down a tree, see our website article "How Do You Decide When to Remove a Tree" by using our website search box.