2005 Crown Vic help with windshield whipers

My dad bought me a Crown Victoria where
from a independent shop, the only
problem that I have with it is the
windshield wipers, which turns on by
themselves, I didn't mind it, but yesterday
the wipers stoped completely, it only turns
on if on the 2 fastest settings, and
wanting to know if anyone knows what
could be the problem and what i should do
from here