03-24-2014 12:36 AM - edited 03-24-2014 12:50 AM
TL;DR: use Display Driver Uninstaller (DDU) from safe mode, after you uninstalled normally.
I accidentally installed the win8 version of the display drivers for Lenovo Ideapad Z575 on a Windows 7 OS and it let me install it just fine, however it didn't work, Catalyst Control Center wouldn't start at all for one (can't remember the details because I forgot to make this post at the time when it happened) and I tried some ways of uninstalling it and reinstalling the latest win7 one again, I wasn't able to. So installing the win7 version after thinking that the win8 version was actually gone really didn't fix the issue. Seemed that the win8 version files remained somewhere in Windows folders and the win7 version being older didn't overwrite the newer version files, so the win7 version was still using some win8 files... I tried uninstalling the win8 version normally but also with a program(can't remember it's name, maybe it was
driver magician? EDIT: nope, it was Driver Fusion, anyway its gui was red+white) which requires booting into safe mode and it deletes some registry keys (but likely doesn't also delete the leftover files).
So, the only way that did work was uninstalling the display driver via Display Driver Uninstaller (DDU)
I don't remember exactly, but I think I ran DDU(in safe mode) after I uninstalled the display driver(catalyst) normally, to perform any leftover cleanup.
Not much more to say, except that this one seems to make sure the leftover driver files are deleted from windows folders and this way the win7 version didn't prevent itself from overwriting newever version files(which weren't deleted by the normal uninstaller for some reason).
Basically, any time you want to install an older version of the display driver you would want to use DDU or else newer version files(ie. c:\windows\system32\atidxx64.dll) will be used mixed in with the old ones(ie. C:\Program Files (x86)\ATI Technologies\ATI.ACE\Core-Static\CCC.exe)
Hope this helps, someone