I just painted my home and it has dried for a week but every time I rub my fingernail over the paint it makes a chalky line. Why is that and what can I do about it?
What sheen of paint did you use? This is typical for cheap flat paints but could also affect dark colors. This mostly happens with low quality paints that don't use good bonding resins or enough resins.
Best thing to do is repaint with a good paint, preferably with a sheen other than flat.