What would cause power to go out in one room breaker not tripped?

When a single room completely loses electrical power but the corresponding circuit breaker in your main service panel remains firmly in the "On" position, the problem points to a downstream break in electrical continuity rather than an overcurrent event. Common causes include a tripped upstream Ground Fault Circuit Interrupter (GFCI) receptacle located elsewhere that cuts power to downstream outlets, a loose wire nut or terminal screw connection that has disconnected inside an outlet box, a broken branch wire, or a faulty switch. You can troubleshoot power failures safely by checking nearby receptacles and testing line voltage with a non-contact voltage tester while keeping safety in mind. You can verify that your corrective action is successful when locating and resetting a tripped GFCI outlet, opening junction boxes to secure loose wire nuts, or restoring faulty connections brings the electrical circuit back to full operational status and restores normal power.