Perfect. I was able to see my HTC One when in fastboot, but not recovery. Forcing the driver as an Android Composite ADB interface did the trick.Do you have the Android SDK installed?
If yes, then you should be able to plug your phone into your computer while in recovery. Then right-click on My Computer > Manage > Device Manager & there will either be a yellow triangle that says "Android" or "Android" should be listed at the top and you would right-click on either one and "update driver software". If it doesn't find it automatically, then > Browse my computer for driver software > Let me pick from a list of device drivers on my computer > Android device > Android Composite ADB Interface.
If you don't have the SDK installed, then install this https://developer.android.com/sdk/index.html and go through the process above.
Should work. Give me a little more info if you can.
Thanks!