Trailer hooked to 115AC. Three circuit breakers, 15, 15 and twenty. On right side, has it's own breaker, suddenly no power to sub -circuits. All receptacles indicate through tester that power is present,however no receptacles or lights will activate. Other two master circuits work normally. What can i do as I have checked the normal things. Circuit breaker O.K and fixtures and receptacles have power. I have not checked the voltage. They all worked up until today.