I had to disable the Compiz fusion thing to get the 'screen' cheat code to work properly, cheat code no3d in 6.2 (Dell Vostro 1710). And desktop LXDE.

You might find out more by looking at the X log. In the old days, X -probeonly 2>&1, or something like that, can't remember exactly, could provide some diagnostic information.
Oh, and could sudo lspci -v avoid the 'access denied's?