If you plug it into an outlet outside of water, do you feel/hear the fan motor turn? If no, have you tried a known working outlet? I'm sure you have but I always start with "Is the power on?"
If the fan turns out and in the the water, then the tube that goes through the fountain wight be clogged with bugs and dirt or leaves. Try a coat hanger to see if you can unblock it.
Threaded Mode
