My tie nail is black and falling off?

Trauma: A black toenail that was bruised and now is dark from dry blood will grow back. You can carefully cut away the potion of the nail that is loose and cover loosely with dr schools foam to protect area until new nail starts to grow. Rarely if the base itself is black back to the area around the base there could be growth underneath nail which needs to be seen and possibly biopsied.

Let it: It sound like you injured the nail. Let it come off by itself and then start using a topical antifungal. The nail will grow back.