An early sign of damaged hearing is temporary deafness after listening to loud music. This is known as the threshold shift and means you have damaged the cochlea in your ear so that your hearing takes time to revert to normal.
Temporary hearing loss or a ringing in the ears is a sign these cells are trying to recover. But over time, recovery becomes impossible and hearing is permanently impaired.
Some people are too severely deaf to benefit from conventional hearing aids; a cochlear implant may be a suitable alternative but only for a proportion of them.