Do you have any 12v
power at all? Lights, water pump, tongue jack?
Make sure your batteries are delivering 12.5 volts up to 12.9. Maybe you have low batteries for some reason. I hope you have a volt meter handy.
If you are connected to shore power, make sure your batteries are receiving about 13.3 volts and even up to 15 volts charging from the converter.
Make sure the cables to the batteries are not loose.
If the batteries are charged, and the converter is delivering voltage to the batteries and thus the 12v
system in the trailer, then you have to dive into the 12v
fuse panel and verify every fuse is ok, not blown. If you find a bad fuse, replace it with the same amperage fuse.