Bad Pom Behavior-Out of Control

Question
My 7 year-old pom's behavior is really out of control. Everytime he suspects my wife and/or myself may leave the house or he hears a noise, he begins to bark uncontrollably without end. My wife and I have tried every trick in the world to calm him down to include special behavior techniques and using a shock collar. Unfortunately, all our efforts were unsuccessful.  We have resorted to ordering him to go into his doggie cage and placing him into a darkened room until he calms down. As our pom begins to bark, he gnashes his teeth and snarls as if he may attack any one of my family members. Our once calm, wonderful companion has turned into menacing disruption both to my wife and baby boy. His behavior has degenerated so much that my wife and I are talking about euthanizing him, a once uncomprehendable thought. Can you please help?  

Answer
At this age I would guess there is more to his problem that
just barking.  Take him to your vet and have him do
a complete health check on him including his ears.  Have
him do a complete blood panel on him as well as check his
kidney's and a urine sample.

Something has changed this old boy that is not obvious to the eye.

Is it possible he is jealous of the baby?  Poms are not
known to be agressive.