Nexus 6 file transfer over USB is not an option

I have a Nexus 6 (just factory reset). When I connect it to my computer through USB, it charges, but nothing else. My computer doesn't recognize any new device being plugged in, and my phone does not pop up with the dialog asking what I want to do (Charge, MTP, PTP, etc.), nor do I get a notification asking this, even when pulling down from the notification drawer. I am running Android 6.0. I have another Nexus 6, and it works fine. When I plug the first Nexus 6 into any computer, I have the same issue, while the second device works fine in any computer. I have tried Windows and Mac computers.