Generator not powering house-already checked breakers/fuses

are you getting power to the 120-vVAC outlets when plugged into shore power?

Start genset, check the receptacle for 120 volts AC using meter or test lamp leads into the blades.
No power means genset power is not getting there. check wiring connections at genset junction box.

do you by chance have an ems? if so does the generator have an unbonded ground? (likely) if so the ems may not let power to the trailer since it detects an open ground.

There are two different definitions of EMS, Intelletec nd Progressive Industries
The PI unit will sometimes not pass Generator power

Likewise your Automatic Transfer Switch, may be fried (if you have one)

Or your manual transfer Device (the plug) came out of the socket.

make and model of generator would be good.

You need to start at the source and check to see where power stops.
1. use tester to see if you have power on generator outlet. If yes, go to step 2.
2. use tester to see if you have power to back of main breaker. If yes, go to step 3.
3. use tester to see of you have power to front of main breaker.
and so on and so on.
When you FIRST have no power where you should have power, you have found the problem. It is between where there is power and where there is no power. You have narrowed it down.

Report back where is the last place you have power and the first place you don't have power and we can help guide you from there.

pianotuna wrote:
make and model of generator would be good.

The OP has an Onan QG 4000...