Comment 5 for bug 743861

"can't move mouse, can't switch to tty, can't send magic sysrq, can't ping the computer from network"

These are more consistent with a kernel lockup rather than X or drm. With gpu lockups, typically the mouse still moves, sysrq still works, and you can ping and ssh the computer from the network.

Check in syslog or kern.log to see if you got a kernel OOPS or some such. Or do a dmesg in a terminal session and then reproduce the error and see if anything gets displayed there. Beyond that, the kernel team may have more specific tips.