I can see you have spent some time to clean and ballance things out, but now is the time to look righ back on anatomy, if anatomicly is what your looking to achive that is. If so il give more help in that area.
I would start with the neck muscles, first being the sternom mastroid muscle(sternom head),this should be attaching to the sternom and the second muscle attatches to the (clavical head.) This is off the top of my head so your need to check for details but at the moment neither muscle is attached to the correct place on your model.