Can access Fastboot, but it isn't working. Software issue?
Since you can start the device and able to enter the Fastboot recovery mode, you can easily flash the stock MotoG ROM. That's all you need to do to factory-reset your device (however, if there is data on your device that needs to be backed-up, that's a different story and perhaps deserves a different post:-))

This is the relevant MotoG forum post for your reference. Summarily, you need two things: The stock MotoG ROM to flash to your device and of course, the MotoG drivers (since you say that your PC is able to detect the MotoG, I guess you already have the drivers installed).

As mentioned in that forum, just download and extract the stock ROM and run the flashall.bat. Your MotoG phone will be as good as new!