The hairdryer is making a rattling noise.
The rattling noise is due to a loose impeller, the plastic part with blades within the device. The noise indicates that the blades are either loose or broken and the blades are hitting the vents. Disassemble the hairdryer and if the part is loose, tighten the blades. If it is broken, replace the impeller.
The hair dryer not turning on/fan not working.
Disassemble and inspect fan blades. If blades are broken, replace them. Test the motor, fan, and switches using a multimeter. If the numbers on the multimeter are consistently changing, then there is a closed path (working). If it stays a constant number, replace the fan, switch, or motor with the same part.
Hair dryer only blows cold air.
Disassemble and find two wires leading to several wounded wires (heating element). Examine the wires and see if there are any breaks in wiring or if debris is clogging the part. Test for continuity. If the circuit is not closed, check the thermal cutout (see below). If the thermal cutout does not have problems, replace the heating element.
Disassemble and check the thermal cutout for any change in color, distortion, and debris. Clean contact breakers (switches) with compressed air.