A computer's cooling fan is directly responsible for maintaining a healthy internal temperature in your system chassis. As excess heat can do serious damage to your internal components, this role is important for the overall health of your computer. If your Optiplex 755's fan has stopped working, it is essential that you replace it quickly. Remove the old fan and take it with you to the computer parts store to make sure you purchase the correct size.
Shut down your Optiplex 755 and unplug all cables from the back of the computer.
Lay the system on its side with the removable panel facing upwards.
Slide the cover release latch out and lift the panel off of the computer.
Attach your antistatic wrist strap to the metal edge of the computer case to prevent static discharge.
Pull the fan's power connector from the slot on the motherboard.
Unclip the fan from the side of the system chassis and remove it.
Be sure to use an antistatic wrist strap to protect your computer from static discharges. One shock can do serious damage to a microchip or drive.