It sounds like the power wire and the neutral wires may be backwards. This happens when these wires are switched around and is called reverse polarity. You didnt say if you had a light kit on the fan also, this would change some of the wiring. Instead of having 3 wires, you will have 4. Black, White, Green, and Red. If no light kit is installed, you will usually not have a Red or have the Red hooked up. Try taking the Black wire and the White wire and switching them around. Be careful and make sure the electric breaker is turned off before doing any of this. Hope this helps, any more questions, feel free to ask.