Here is my suggestion.
If the peg board is removable remove it to find any GFCI back there.
You said there is GFCI braker. Make sure you have voltage on the downstream side of that GFCI breaker.
Kitchen GFCI.
Maybe a GFCI covered with an appliance,poster,cabinet...anything.
Check for continuity at the nonpowered receptacle between Grounded(neutral) and grounding. If there is no continuity then there is a GFCI problem if there is continuity then there is loose connection of the hot conductor.
I will post if any other ideas come up
P.S. I had the same problem could not find a problem to a bathroom receptacle. Come to find out the GFCI that powers that bathroom is in the garage behind a poster. It took me 2 hours to find it. Then i had to explain to the home owner why i charged him $120 to reset a GFCI.
Good Luck
Edward
