The answer to 'why is my GFCI outlet not working' is that there are several common causes, including a tripped circuit, faulty wiring, or the GFCI outlet itself may be malfunctioning. GFCI outlets are designed to trip and cut power when they detect a ground fault, which helps prevent electric shocks. If the GFCI is tripped, you'll need to reset it by pressing the 'reset' button.
Other possible issues include loose or damaged wiring connections, a GFCI that has reached the end of its lifespan, or a problem with the circuit breaker. In some cases, the GFCI may need to be replaced. If you're not comfortable troubleshooting the issue yourself, it's best to call a licensed electrician to diagnose and repair the problem.