Why is the flowers all gone brown and the leafs are looking that they are dying is this common this time of year
It had fruits last year very nice a sweet
Do the branches snap off and break?
Do the branches bend?
You can do the scratch test to check if the tree is alive.
If the tree was exposed to cold temperatures, it could have killed off the buds. If this is the case the tree may look bare for the year and then leaf out next season.
You can then prune any dead material next year from the tree.
I am concerned about the concrete the covers the root system of your tree. The trees roots need oxygen and if covered in hard surface material they are not able to get this necessary element.
Plum trees have lots of roots near the surface to help with water and nutrient collection.
If the root system is covered in concrete the tree may die off.