PoE regulates its voltage by detecting certain resistive amounts when a device is connected. Whacking a voltmeter onto the patch cable is probably going to give you bad readings.
The 3' patch cable is a good start. Since I assumed that failed, the next step would be to get you and/or the electrician on the phone to QSee tech support to help walk him through. QSee is just a Costco-style brand, so don't expect the Earth, but their support is probably going to be the fastest way to diagnose a problem that neither of you are familiar with.
Also, Luis above has probably sent you a very helpful PM :)
