Unfortunately, your plant looks dead. Once a plant is dead it is difficult to determine why.  May be possible poor drainage, soil compaction, planting too deeply, possible cankers, etc.
It would be helpful if you could submit photos as soon as you notice symptoms on your plants so we can see what you may be dealing with.  Scratch the branches with your fingernail and look for green tissue for any signs of growth. If you see brown/gray it is dead.  
mh

I do agree that the plant is dying.  The photos previously sent were branches that were pruned away.  About 1/3 of the plant is still alive.  Is it worth trying to save what's left?  

Sure. It's worth trying to save what's left. If the roots are healthy, it may try to send up new growth from the base.
You'll just have to wait and see.

cm