You are called to look at a co-workers computer. It is not powering on, no fans start, there is no sound, and no lights turn on when the power button is pushed. What should you do first?
Checking the power cable is the most logical answer. You do not know if the power supply is good yet, so replacing it would be premature. These symptoms are not indicative of a CMOS battery issue or a boot sequence issue (also, you can't access the BIOS/UEFI if there is no power).