Somehow I have fixed whatever was going on. The first thing I did was to uninstall the old Windows 8.1 drivers. AMD no longer supports Windows 8.1 and has stopped making drivers for their cards for that OS; the last Windows 8.1 driver was on 7/14/17. I installed the Windows 7 drivers instead. But that did not fix my issue with the game initially. I then deleted the app data folder just now and the game started working. I have done this before without any success since installing the W7 driver so I don't know why it worked this time.