The lights flickered because the lights inside are 12 volt and the generator starter motor draws CONSIDERABLE amprage so it "Drew down" the house system voltage.
As to why it did not start: Multiple possible reasons
First the fuel supply. Generally the generator can not use the last 25% (1/4th) of the fuel in the tank (Makes sure you have enough to get to ye old gas station) If the batteries are NOT connected there might not be enough oomph in the converter to crank it fast enough.
Operator error
Bad problem with generator needing $$$$ to fix.
