Final answer:
The first thing to do is empathize with the customer and assure them of help. Then, ask if they have tried basic troubleshooting steps. If the issue persists, escalate or offer a replacement.
Step-by-step explanation:
The first thing you should do when a customer complains that their computer will not start-up is to empathize with their frustration and assure them that you will help resolve the issue. Ask them if they have tried any troubleshooting steps, such as checking if the power cable is securely connected or pressing the power button properly. Walk them through these basic troubleshooting steps and if the issue persists, it may be necessary to escalate the case to a technician or offer a replacement if the computer is still under warranty.