A technician is troubleshooting a computer with a suspected short in the power supply.

The first step a technician should take when troubleshooting a computer with a suspected short in the power supply is B. Disconnect the power before servicing the PC. This is to prevent any electrical shock or damage to the components. A power supply can be dangerous even when unplugged, as capacitors can maintain a line voltage charge for a long time1. Therefore, it is important to disconnect the power cord and press the power button to discharge any residual power before opening the case2. The other steps are also important for safety and proper diagnosis, but they should be done after disconnecting the power.