First remove the outside inspection cover and look for greenish goo and/or smell of ammonia. If you see greenish goo and/or smell ammonia, immediately unplug the fridge and DO NOT USE. Fire risk.
If that's clear then try the steps below.
Try shutting the fridge OFF completely and then turning it back on. If that doesn't work, unplug the fridge completely and let set for 3 minutes, then plug it back in. Finally, make sure your batteries are fully charged. The fridge needs 12V power to turn it on....there's other tests if this doesn't work....Dennis