Not sure of your level of expertise so replies above may be hard to follow. Forgive me if this is too basic. The chassis battery that starts the engine is separate from the house batteries. Also If you are plugged in to shore power the RV house will work even if batteries are dead. Best solution is testing both battery sets with a voltmeter. If not possible I would check to be sure use switch is "on" while plugged into shore power, as suggested above. If voltmeter shows all batteries have 12 or more volts then come back for more suggestions.
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