Win10 sucks with drivers for the OnePlus.
I don't really think it is a driver issue when you are in command prompt / adb. As all the other commands work fine.
fact is, I did not install any driver and my Windows 10 installation detected and installed everything automatically
adb and fastboot worked from "the box"
The drivers are needed when you plug your phone in while it is booted properly such that the device says "USB connected" in notifications and lets you choose "transfer files" and what not. That driver exe file is shown the first time you plug in the phone while booted and one has to do this each time a new devices comes out (as I just had to do last week when my OP5T arrived even though OP5 drivers where already installed)
Anyway, like I sai, find an old computer for sideloading and kids...never ever ever RELOCK your device, despite what the stupid message says upon boot or you'll end up like this guy.
Did you verify Fastboot drivers are recognized by typing fastboot devices at the command prompt while your phone is in Fastboot Mode? If not follow the directions below.
If you're using Windows 10 make sure you manually add the directory where adb and fastboot is located. Under Environmental Variables
1)System Properties->Advance->Environmental Variables->
2) Under "User variable for your login name"/ and "System Variables"click Path then Click Edit. You want to do this for both system/user variable.
3)Under "Edit environmental variables" choose New and type the directory you install the adb /fastboot files in.. Don't know shift +Right Mouse click will give you directory
Here is a link with pictures https://www.xda-developers.com/adb-fastboot-any-directory-windows-linux/
Linage has a great tutorial on installing TWRP https://wiki.lineageos.org/devices/cheeseburger/install
Once you get this installed you should be a to side load oxygenos onto your phone
UPDATE- PROBLEM SOLVED!!!!
As per Dax's suggestion, we contacted oneplus and a technician contacted us and done a remote session. He got us to connect the phone in qualcomm mode (by turning it off and then holding volume down then connect usb cable while still holding button) and used Msmtool with a file from oneplus that contained dumpling_43 rather than cheeseburger_23 in the filename. No idea where to get these files as the zip they had me download was password protected. After they were done they deleted the files, now the phone works fine...
By the way, Thank you everyone, for all of your help and support! If it was not for the help from this forum, I would have been totally stuck with no idea what to do, and would have probably ended up giving my phone to the "will it blend" guy.
Glad to hear it!
That's good to hear. I'm happy for once something useful came out of this forum
Flash stock recovery with adb/fastboot and sideload stock image via adb
[Contest] OnePlus 4th Anniversary - My OnePlus Story
by David Y., 2017-12-12