At this time of year, crape myrtles are generally going to be bare, as they are deciduous. Browning of leaf tips might be a result of excessive fertilization or salt injury, or possibly a foliar disease. Sparse flowering might be a result of insufficient nutrients, improper pH, or not enough sunlight.
There are a lot of possibilities here that will need some additional diagnosis to solve.
I suggest you contact your local Pinellas County UF/IFAS Extension office in Largo for additional assistance. Here is their contact information: http://pinellas.ifas.ufl.edu/home_landscape/index.shtml