You said: THe only thing that works is the 12 volt lights when plugged into shore power.
Well.. Though there are exceptions.. One I know for sure is the Magnetek 6300, On most RVs this would indicate the converter *IS* working.
On the 6300 however there is a relay and perhaps a fuse that is NOT working.
On most all RV's there is a fuse or circuit breaker in the battery lead, either near the battery, the Battery control center, or the converter,, This too may have either Operated (Fuses, operated = blown) or malfunctioned (Breakers).