Fan not working! Please help!

Well, I searched and I didn't find anything, so if this has already been addressed, I apologize.

Something is wrong with the fan in the air-conditioner/heater. The other day, Jimmy turned on the heater and the little knob fell off. No big deal, but when we put the knob back on, the heater stopped working. At first, Jimmy thought it had gotten turned wrong because the knob would turn the wrong way. But then I figured out he had not put that little blue piece back in that stops it from turning all the way around. So we fixed that, but it still wasn't working right. When you turn it on, you get nothing at 1, nothing at 2, but 3+ all work fine.

Has anyone dealt with this? It wouldn't be so bad if it were the other way around, but to have to set it at three all the time is really annoying! Please help if you can!