From our symptoms, I have to assume you have a motorhome with a built-in generator?
If this is the case then I also have to assume that the generator runs but your Rv does not switch over to it for 110-VAC power?
With these two conditions being true, then you should know that your motorhome has a "transfer switch' which is actually a solenoid that your power management panel used to select either the external power or the generator for power. Two AC power sources cannot be tied together so this transfer switch doe the job for you. When the power control panel senses that the generator is running and generating power, then it switches over to the generator as long as it is running.
So, check two things first;
1- is your Coach battery fully charged? If not, your Power Control panel will not operate properly. If the battery is OK, then you may either have a bad "power generator" portion of your generator, or
2- you could have a bad transfer switch. The transfer switch being bad is the most common cause of your problem.