sense i don't know ur trailer, lets start with the basic. do u have 12v? ie do ur interior lights work.
if there is a red turn key (mine is on a chain) close to the breaker box, try it in a different position.
i will ask a few questions to see where u r. maybe someone that knows the trailer will chime in with the correct answers.
if u have the disconnect, they separate the battery form the converter and the dc part of the trailer (usually the slides are connected to the battery).