Installing AMD GPU drivers slows my Windows 8.1 system to a crawl

I have a Windows 8.1 system and an AMD HD Radeon 7970 graphics card that appears to work fine (it plays modern games without issue). I've used the up-to-date AMD drivers for some time, updating them a few times since I built the system last year.

Every now and then, starting a few months ago, my computer would slow down to near standstill. The hard drive access light would be on nonstop while the computer was slow. Rebooting would not fix the issue, and boot times would go up to 30 minutes. Every time the issue goes away, there's no apparent reason for it to have gone away. The issue is now reproducing 100% of the time.

At first, I thought it was a hardware issue with either the mobo, SATA cables, or driver. I switched ports and cables and ran disk checks. No change. Then I thought it was malware, so I scanned the computer with Malwarebytes and Spybot. No serious threats.

Then I discovered the computer boots very quickly into safe mode. I also discovered that if I completely remove the AMD GPU drivers using Display Driver Uninstaller my computer would boot very quickly into normal mode. I assumed this meant that there was something wrong with the recent AMD drivers I was using (15.6 beta and 15.7), so I've now tried using older AMD GPU drivers (since my system worked fine for many months on some 14.x version), but I still get the same issue with 14.12 and 13.12.

I've also tried disabling Windows update and using different AHCI drivers in case there was some weird incompatibility with the GPU drivers.

Does anyone have a guess as to why my computer runs fine without the graphics driver but then my computer slows to a crawl after installing any AMD GPU driver? Or why installing the driver would change non-graphics intensive functions, like booting, to have 100% disk access? Any guesses on how to diagnose the issue from here would be valuable.

Answer

I have apparently resolved the issue by not only uninstalling the AMD drivers, but also uninstalling all listed drivers in Device Manager under "Display adapters" while in safe mode, then rebooting normally and reinstalling the latest AMD drivers. I still don't know what caused the issue exactly, but I've not experienced the issue for one week now.