I have been replacing all of the outlets and light switches in our cottage. Cannot get one GFCI wired properly. There are two black and two white wires with a ground. My tester shows that one black wire is hot. After no success with the GFCI (and a replacement just in case the GFCI itself was defective in some way), I tried just wiring a regular outlet with two and then all four wires, and still no power. Is there anything else that I can check, or have I reached the point where I need an electrician? I can't figure out how I have a hot wire, but still no power?thanks