I've been trying to root my OnePlus One for two days now and I've continued to have this issue. After installing Android Studio + the SDK, as well as downloading the Google USB Driver, when I connect my phone to my computer it shows up as an MTP device under unknown devices.
If I allow it to automatically download drivers, it becomes a portable device instead. But I need it as an ADB device. I've already started USB debugging on the phone, as well as switching between all the different USB options on the phone (charging, MTP, PTP, MIDI, etc.), and still no good.
When I try to update the driver for the "MTP" device, the Google USB drivers don't show up, and if I try to browse manually, it comes up with the error message saying how "the folder you specified doesn't contain a compatible driver."
What do I do?