Sorry for the delayed response and I would imagine that you've already found a solution. But A make sure you've downloaded the Moto driver to your PC. It's something that should come from the phone when you first connect it to your PC if it fails to find the driver. But you can also hunt around on any number of places and find it yourself.
And B, when you do connect make sure to pull down the Notification shade on your device. It defaults to charging only and the second selection will allow you to transfer files.
Otherwise look for USB Debugging although I haven't had to use USB Debugging in quite some time so I don't know where you'd find it or if it would make a difference.
Consider powering down and removing the SD card, it might be damaged, corrupted or otherwise incompatible. If it's fine then invest in an SD card reader/writer if your PC doesn't have one built in. Just transfer your files directly.
OR do what I and I'm sure others have, use something like Google Drive or Drop Box as a middleman. I rarely if ever physically connect me G5 Plus and my PC to each other anymore, since getting into Google Drive. I use Drive to move files, pics and music between my device and PC. If you have a Gmail account, and because you have an Android you do, then you also have a Google Drive account...