There have been some frustration upon AMD/ATI's current decision to drop proprietary driver development, in favor for open source driver development.

Not the decision per se, but the outcome for some ATI users is frustrating: Many older, but not to old, Graphic-Cards do not work anymore, due to normal updates, on supported version.

So, what is the deal here?

The deal here is AMD/ATI completly dropping development of the old driver and Linux development going forward. The now old AMD/ATI drivers need xorg 1.16 to function properly, but at some time mid 2017 Canonical decided to update even ubuntu 14.04's xorg to 1.18 and all the old drivers broke. Leaving users with slightly older cards with xorg config or even black screen on startup, without a warning beforehand.

Let's focus on the solution.

The solution is to downgrade xorg and respective packages and dependencies to a version where the proprietary AMD/ATI driver was working, with this command:

sudo apt-get install xserver-xorg-lts-utopic libqt5gui5 libgles1-mesa-lts-utopic libgles2-mesa-lts-utopic libgl1-mesa-glx-lts-utopic libgl1-mesa-glx-lts-utopic:i386 libglapi-mesa-lts-utopic:i386 libegl1-mesa-drivers-lts-utopic

(source: Askubuntu)

Ok, you might notice you "downgrade" 14.04LTS with packages from "utopic", which is the 14.10 (non-lts) version of ubuntu. I am also confused about this. Please do not ask. I am not sure what this is about, if you know, please leave a comment below.

At least at the "Problem Machine", an Asus Laptop with Radeon 6850M Card, this enabled me to activate the drivers from the "Additional Drivers"-Menu and everything (Minecraft in particular) was running fine again afterwards. You could also install these drivers from the command line, like this:

sudo apt-get install fglrx-updates

Have fun. May the code be with you.