You do not state which fan it was but if it was just a case fan then it will have no bearing ion whether your PC will start or not. If it was the fan on top of the heat-sink covering your processor then yes it will probably stop the PC starting if it was not reinstalled correctly or plugged in to the correct header on the motherboard.
If you have a noise in your PC then remove the side and try and listen to where the sound is coming from. You have done the right thing by removing the build up of dust but in doing so you might have knocked another connection so try every cable in your PC and make sure that they are all seated correctly. Also make sure you have not dislodged a component such as your memory (RAM).
If it still does not work we will have to think of other causes.