A user replaces their PC power supply and connects it to the components, but the...

Modern motherboards require both the 24-pin ATX connector and a 4-pin or 8-pin CPU power connector. If the CPU power connector is not attached, the motherboard will receive power but the system will not boot. CompTIA A+ specifically lists this as a common mistake after replacing a power supply.

Insufficient wattage may cause instability, but usually the system still attempts to start. RAM does not prevent power-on if missing; instead, the system produces beep codes. Redundant PSUs are used in servers, not standard desktops.

Therefore, the missing CPU power connector is the most likely cause, and this scenario reflects typical troubleshooting steps outlined in A+ hardware diagnostics.