Not sure about your LP Generator...I like most have a diesel (or gas) generator. First what is the manufacturer and model? Any Error Codes? Our Onan 7800 watt operates as thus. To start you must push DOWN on the start switch to PRIME the system. The light within the switch flashes rapidly. You should hear the pump running too. Do this for a few seconds Next push the same switch UP and I count 13 seconds and if the generator has not started in months, after a count of 13 seconds, it fires up.
If the fuel system is empty or lots of air it will take several attempts to get it running. BUT don't just keep cranking! You will ruin the starter, wiring, etc. After cranking, wait 5 minutes so the starter can cool down.
Keep us posted!
John & Debbie
2008 Fleetwood Discovery 40X