It just happened again (virtualbox-ose is not installed), but this time the symptoms changed. The screen shows a corrupted image, goes black, shows a corrupted image, goes black, and so on. Switching to another VT did not work, but I was able to reboot the system with the sysrq keys.
** Changed in: xserver-xorg-video-ati (Ubuntu) Status: Incomplete => New -- [RV730XT] sporadic freezes https://bugs.launchpad.net/bugs/557688 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs