Comment 10 for bug 114520

Did you try with device section as proposed in comment 6 ?
Please try this, you really have too much options; so it's
hard to understand from where the issue likely come.

Btw i am not sure i fully understand your issue, you have
a black screen after some times, is this after some times
of inactivity ? If so then this likely somethings related
to dpms and failing to wake up the card or the screen.

Anyway the fact that ctr-alt-backspace restart properly your
xserver likely mean that the isn't lockup at all.