Hello there, just a couple of thoughts!
1. Confirm that your unit actually has one and not just Inverter preped.
2. Ensure 12 volt main disconnect is on and your battery or batteries are charged
3. Do you have a remote mounted switch for the inverter? Ensure it is on. If not, you likely have a local on off switch at the inverter itself. Ensure it is turned on locally.(Not sure where it is located)
4. Ensure your breaker and fuse panel has breakers on and no blown fuses.
5. A transfer switch would also be involved that would change the path from shore power to inverter power, ensure it is operating.
Hope this list help you get to the bottom of things.