I had a simular problem with my 28a+. There are 2 30amp circuit breakers under the front of the trailer. Just behind the hitch A frame. If you lay on your back and follow your battery wire through the frame you'll find it. You can test the breakers with a test 12v test light. Here is a picture of the breakers
Terminal 1 is your 12v power source coming from the converter( red wire) and the black wire goes to the 7 pin connector.
Terminal 2 doesn't have a wire on it. There is a jumper plate going to terminal 3 (connecting the breakers together)
Terminal 3 is your battery connection.
Terminal 4 is your slider connection.
I'm guessing that the breaker on the left of your trailer is gone or needs to be reset. Unplug the trailer from powercord and the TV. Connect a test light to a good ground. If you have the battery connected, you should get the light to come on when you touch terminal 3. If it doesn't the battery is dead, or you didn't get a good enough ground. Once you get past that, all 4 terminals should have 12v to them. If any terminal don't have 12v then disconect positive wire from the battery. The trailer shoud have no power. Tap the breakers with the back of a screw driver( one of the breakers might be stuck) . Reconnect the battery and see if 12v has returned to all 4 terminals. If there is no power between terminal 3 and 4 then you need to replace the 30amp breaker on the left. The right breaker on my trailer had tripped and the above proceedure reset it.