GFCI will not reset if there is no power to it.. Start with the circuit breaker that feeds it and make sure it is delivering power, then start tracing wires.
GFCI will reset, but will insta trip, if there is a down-line ground fault.. To test this Remove GFCI from wall and disconnect the wires attached to the LOAD leads.
GFCI also will not reset if you confuse LINE and LOAD terminals.
Power comes into LINE, and exits to other outlets via LOAD
NOTE: in the following process I do not talk about turning the breaker on and off, you should do this when connecting and disconneting, I like to use test leads with clips when working with 120 volt so I can power off, hook up power on take reading, power off and move to the next step... USE CAUTION when playing with 120 volts.. Folks who do not use caution often end up mentioned on Wendy Northcutt's web page.. www dot darwinawards dot com.
So Check breaker to make sure not tripped
Check to make sure power passing through breaker
Make sure screws (All of them in the breaker box) are tight,, Don't laugh, but many RVers have a few screws loose in this compartment.
Check for power at the GFCI LINE terminals. NO power = what you got.
Make sure you have not confused the two power cables there.. (Check for power on the other set of wires) hook the wires with POWER to the LINE leads on the GFCI, it should now reset if power is present.
Finally connect the LOAD lines, if it now insta-trips check your patio outlet for moisture, often these fill with water and insta-trip the GFCI.