If you've got it "switched" to 110 or 12v and it doesn't power up, it could be fuses...
My 12v fuses are in the 12v line that feeds the fridge
I'd try a 110v test first, though:
Have you tried plugging the fridge
in to 110 directly?
By this I mean, look inside the outside access door and you'll see that the fridge
is plugged in to a 110v outlet inside the compartment.
Unplug it and plug it in to an extension cord to 110 power.
Give it some time before you decide whether it's cooling or not.
If it works by this method, you probably have a trailer wiring problem.
Hope this helps!