I have a Onan 7.5KW Diesel generator and then same thing happened to me. On the top of the generator next to the start switch is a lever/button which is very easy to accidentally turn off. You might want to check that out. I have hit that switch a number of times and the generator motor runs but no electricity.
The generator won't run unless it is producing electricity. It shuts itself down if it doesn't see 120 vac being produced. All Onans have a breaker and many have two. One for a 30 amp winding and one for a 20 amp winding. When you find them make sure you turn them off and back on to reset them.
Clay (WA5NMR), Lee (Wife), Katie (cat).
Full Timing in a 2004 Winnebago Sightseer 35N, Workhorse chassis, Honda Accord toad
Had my onan doing the same. Hit all the breakers I could find, even changed out the automatic switch. Finally took it to an onan repair shop and turns out the brushes were dirty and not making contact. Cost me about $200 to do something I could have done had I known.