R9 390 drivers would not install via auto-detect software. Failed at 99% with SUCCESS everywhere except at the "Final" step (in log).
OS:
Windows 8.1
Solution:
1. In Device Manager, disable (not uninstall) Display adapters > Microsoft Display Adapter
2. In Device Manager, disable (not uninstall) Monitors > Generic PnP Monitor
3. Make sure all partial installations of AMD drivers are uninstalled
4. During installation, keep device manager open and disable any drivers that revert to a normal state (i.e., no longer disabled)