Possible problems:
1: Batteries disconnected (Store mode. Aux off, Whatever)
2: Fuses blown Battery main, or converter (To test disconnect batteries with interior lights on. if they go out (Perhaps after a period of time like 1 minute or less) converter side issues If they remain bright. Converter good)
3: There are fuses on the converter if it is a stand alone. if it's part of the power distribution panel (Fuse/breaker box) then they are USUALLY (not always) the fuses on the right. also USUALLY 30 amp but again not necessarly. ALL reverse polarity fuses must be replaced at teh same tiem while UNPLUGGed from shore.
4 Fried convreter (I have a fried converter if you want one :) )
5 Now... MY converter is a Progressive Dynamics 9180 Plug in model with wizard. Why do I tell you this.. From time to time the first one failed. Not sure if the replacement failed but there were two kinds of failure.. The last failure of the first one was "Fried converter replacw"
The earlier failures were the old "lady I think I see your problem already"
Plug - - - - - Socket
Restored the plug to socket and all was good just like magic.