The user turns on the computer and hears a popping sound and detects a burning smell. The system will not power on. Which of the following is the MOST likely problem?

A power supply failure often produces a distinctive popping noise (from a blown capacitor or other failed component) along with a burning smell from overheated or burned components inside the PSU. Since the PSU is the source of all system power, its failure results in a complete inability to power on the system - these are the hallmark indicators of PSU failure.

A faulty CPU fan would cause thermal shutdown or CPU damage over time but would not produce a popping sound or burning smell immediately at power-on.

Motherboard overheating typically causes unexpected shutdowns or POST failures during operation, not a popping sound and burning smell at initial power-on.

A tripped UPS (Uninterruptible Power Supply) would cut power to the system but would not produce a popping sound or burning smell originating from within the PC.