Deafness caused by the inner ear
There are various ways that a person may become deaf. One way is if the hair cells in the cochlea are somehow damaged or not working and cannot send impulses to the auditory nerve fibres.
In many cases, the auditory nerve fibres are still intact and functional, but are not responsive because they are not receiving any impulses from the damaged hair cells.
Can't a hearing aid help?
A hearing aid works by making sounds louder and/or clearer.
However, if the hair cells in the cochlea are severely damaged they are incapable of sending impulses, no matter how loud the sounds are.