having recurrent trouble running (k)ubuntu on a dell vostro 3555 using a radeon hd 6520g chipset, i'd solved those on 13.10, re-installing the proprietary driver (because the resume on lid open and resume after sleep were not functionning with the free drivers).
but since the upgrading to 14.04 (kubuntu still) i cannot have it working nicely, wether with free drivers (no open gl, 3D, no resuming after sleep or lid closing/opening...), and neither with fglrx proprietary drivers (things work more or less, but after resuming from sleep or pause i have a very low backlight, no control on the brightness via menus or function keys until i logout/login)
So, if somebody would suggest a solution i would be quite happy of it because spending time searching for solution is not my favourite hobby, my linux/computing skills are restricted to a short knowledge and comprehension, sorry about that !!!