Since most lights use 12v DC along with the frig., it does seem like you have a 12v DC problem. The converter may have failed, tripped it's input breaker (which is 120v AC) or blown a 12v DC output fuse. And then the battery would discharge, so as suggested, check the battery. If it is dead, put a separate battery charger on it as a temp. fix. Then locate the converter and check it's output. Finally check for 120v AC power to the converter.
Also, you probably have 50 amp shore power which means there are two 120v legs coming into the RV. It is possible that one leg is open, either at the camp pedestal, at either end of your shore power cord, or at the connection on the RV. Anyway, if one leg is open, some 120v AC items will not work since they are using that leg and other 120v AC items will be fine. So check all items that need 120v AC, like both air conditioners, every single outlet, etc.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK