Which Xorg driver are you using (radeon, radeonHD, fglrx, etc.)?
Please also attach the contents of /var/log/Xorg.0.log from a session where this problem occurs, and the output of lspci -vvnn
Which Xorg driver are you using (radeon, radeonHD, fglrx, etc.)?
Please also attach the contents of /var/log/Xorg.0.log from a session where this problem occurs, and the output of lspci -vvnn