This is a peer to peer forum not a direct link to support. Call them from a different phone 800-922-0204 or 611 from a DIFFERENT Verizon cell.
It could be that when you plug your phone into a usb port on your computer, the phone is in charging mode. If that is the case, pull down the Notifications bar at the top of the display and select USB Charging. You will see various options.
I am having the same problem. If I connect my S6 via USB I can drag and drop photos to my computer. When I connect my S7 with the same USB cable, select file explorer, select the Samsung device, select open, select DCIM, select camera the photos will come up. If I then try to drag and drop one to another file I get a message that says A device attached to the system is not functioning. I have downloaded the S7 software and also updated the S7 drivers from the Samsung website. I also went into settings enable developer options and turn USB debugging on as some have suggested but that didn't work either. I have selected file transfer in the phones drop down menu. I have also restarted both the phone and computer. Still doesn't work. The computer is Windows 10. I have run out of things to try. Any suggestions?
Your S7 works differently than your S6. As I said above, when you plug your S7 into a usb port on your W10 computer, the phone will start to charge. You should get a warning that the phone will charge faster with the original charger. You will see a usb charging notification that if selected will give you file transfer choices. If you have the software installed,Windows will ask you the same thing.
If you see nothing, there may be a problem with the cable (yes, I know it worked on the S6) or the usb port on your phone.
Try a different cable. Also try the usb adapter that came with the phone with a flashdrive as a way to test the phone.
I have changed the USB port from Charging to MTP. downloaded drivers and Samsung Smart Switch. I'm fairly sure the phone's USB port is the problem. Samsung was no help. The Verizon tech took me through testing and configuration changes. I will try to find a Samsung test Center to run diagnostics on the phone. if there is an app or software I can download or buy to allow me to do diagnostics let me know.