If it's the keyboard you might be able to fix it by raising it 4"-6" from a flat surface, turning it over so that the Keys are facing down and letting it go. If that does'nt work replace it.
If it is a cable inside the PC that is hitting a Fan, shut the PC down and turn off the Power at the oulet and remove the Power cable. Remove the cover from the Case and remembering to ground yourself by placing the back of your hand on the Power Supply Unit and not moving your feet. By not taking this precaution it is possible that you could inadvertantly cause damage to the PC from an electrostatic discharge.
Do a physical check of Cables around the Fans to make sure that they are not touching. If they are they can be held out of the way by using plastic Cable Ties. Do not use Glue, BlueTac, Paper Clips, Paper covered Wire strips or Elasic bands.
While you are there I would give the inside of the case a blowout with compressed air and use a small soft bristled paint brush for the stubborn stuff. When blowing air through the fans make sure that you physically stop them from spinning, as they may generate power and blow something up.