What is the best course of action if your power supply's fan no longer works?

Replace the entire power supply. You cannot repair your desktops power supply; you can only replace it. You should not ever open your computer power supply or try to fix it yourself.

If the power supply is restricted, you may need to loosen the screws holding some drives in place and pull them forward a little. If the power supply still doesn't come out, make sure you have removed all the screws. Some power supplies have extra screws around their base to hold them down. If you are planning to add more computer gear, a powerful graphics card, more hard drives, or more DVD burners, buy a power supply with a higher wattage.