A few years back I installed 2 GFCI circuits in a kitchen remodel job. The first outlet worked, tested, and reset as designed. The second one did exactly what you describe (would not reset). After spending some time checking, tracing and testing wires I concluded the the outlet itself was defective. To make a long story short, I made 2 more trips to the Big Orange Box store only to come back with 2 more defective GFCI outlets. I ended up going to a local, family owned home improvement store, paid a dollar more for the outlet, but this one worked.