Hey Steve, welcome to the real runner's world! If your toenail is black and traumatized, still sore, it's most likely got blood pooled just under the nail. See a specialist to get it drained, and to prevent future problems, do as all the others have said and ensure your shoes and socks fit properly. Oh and don't slam your feet when running downhill, try to flow freely and not brake too much, this causes your toes to get jammed against the front of the shoes, hence the bruised nails.
Sheila