The troubleshooting step being used when the technician leads the caller through checking power cables and power lights is "Identify the problem." Explanation:
At this point, the technician is trying to clarify and confirm what the caller means by "the computer will not turn on" by ruling out simple issues such as loose or unplugged power cables and checking if the computer is receiving power (indicated by power lights). This step focuses on understanding the exact nature of the problem before establishing a probable cause or implementing any solutions. Once the problem is identified, the technician can then proceed to diagnose and resolve it effectively.