In my case situation improved a lot removing the /etc/X11/xorg.conf file and following the advices here :
https://wiki.ubuntu.com/X/Troubleshooting/FglrxInteferesWithRadeonDriver#Problem:%20%20Need%20to%20fully%20remove%20-nvidia%20and%20reinstall%20-nv%20from%20scratch
In my case situation improved a lot removing the /etc/X11/xorg.conf file and following the advices here :
https:/ /wiki.ubuntu. com/X/Troublesh ooting/ FglrxInteferesW ithRadeonDriver #Problem: %20%20Need% 20to%20fully% 20remove% 20-nvidia% 20and%20reinsta ll%20-nv% 20from% 20scratch