Here’s a generic driver and ADB/Fastboot repair …
- Disconnect the phone from the computer.
- In Control Panel - Programs and Features:
Uninstall the Android SDK (if installed) and everything with “MTP” or “ADB” in its name.
- Reboot Windows.
- In Control Panel - Device Manager:
Enable View - Show hidden devices, and then uninstall every possible ADB, MTP and smartphone device, hidden or not.
- Reboot Windows.
- Connect the phone again. (Windows should install the necessary drivers then automatically. They can be named after a different device, this doesn’t matter.)
- Download the current Android SDK Platform Tools
- Unzip the ZIP file to e.g. C:\platform-tools (you can unzip it to wherever you like).
- Add the path to where you unzipped the tools to the Windows “PATH” environment variable , so adb and fastboot could be run from everywhere without always having to prefix them with the path.
Then try fastboot devices again.