I recently downgraded my Ubuntu to 12.04.5LTS because I wanted dual monitor support but my hd4870 cant support AMD drivers and stuff.
Once I downgraded it and tried to install the drivers something like "one or more tools required for installation are not on this system" or something.
I looked online and tried a few solutions but none of them work like. I don't remember all that I did but these are among them.
Install headers, 32bit lib.
Check if system has the tools required for installation. fglrx installation requires that the system have kernel headers. /lib/modules/3.13.0-61-generic/build/include/linux/version.h cannot be found on this system. One or more tools required for installation cannot be found on the system. Install the required tools before installing the fglrx driver. Optionally, run the installer with --force option to install without the tools. Forcing install will disable AMD hardware acceleration and may make your system unstable. Not recommended.