Firstly try revert to the "old" xorg.conf before fglrx was installed. If you used `aticonfig` to create a new xorg.conf, it would have created a backup of xorg.conf as xorg.conf.original-0. If that backup file is empty then you can just delete the current xorg.conf.
Also check /etc/modprobe.d/ for configurations that blacklist the open source driver "radeon".
You might also would like to
reinstall mesa-related packages.
Fglrx itself as a dead object is no longer installable atop the current kernel and Xorg.
g1annos wrote:Cannot login to Desktop after Stretch upgrade
Do you mean a login loop or no login screen at all?