This sounds more like Xorg is crashing rather than a gdm problem. Please attach /var/log/Xorg.0.log and /var/log/Xorg.0.log.old after this happens
This sounds more like Xorg is crashing rather than a gdm problem. Please attach /var/log/Xorg.0.log and /var/log/ Xorg.0. log.old after this happens