To see nails in your dreams, indicates much toil and small recompense.
To deal in nails, shows that you will engage in honorable work, even if it be lowly.
To see rusty or broken nails, indicates sickness and failure in business.
Depending on the content of the dream, hammering might represent feelings of anger and hostility or you may be reflecting on hard work and honorable endeavors.
Additionally nails may have some sexual connotations.
A man may be expressing some repressed anxiety about sexual potency while a woman may be expressing her unconscious abhorrence of sex.