A user hears an unexpected noise coming from their desktop computer.

The correct answer is C. Disconnect the power , because safety is the first priority when working inside a computer case. Before opening the system, all power sources must be removed to prevent electrical shock and hardware damage.

According to the Quentin Docter – CompTIA A+ Complete Study Guide , technicians should always shut down the system and disconnect the power cable before opening a computer. Even powered-off systems can still carry electrical current if they remain plugged in.

The Travis Everett & Andrew Hutz – All-in-One Exam Guide explains that unexpected noises are often caused by fans, loose cables, or failing hard drives. Opening the case while the system is powered can cause injury or damage sensitive components.

The Mike Meyers / Mark Soper Lab Manual reinforces the standard safety sequence: power off the system, unplug it, discharge residual power, and then apply grounding measures before touching internal components.

Because disconnecting power eliminates electrical hazards and protects both the technician and the equipment, C is the correct answer.