Comment # 8 on bug 76659 from Alex Deucher

Does manually turning off the display also cause problems?  e.g. run:
xset dpms force off
xset dpms force on
from a terminal

Can you get remote access to the box (e.g., ssh)?  If so can you try manually
turning the displays on/off?  E.g.,

DISPLAY=:0.0 xset dpms force off
DISPLAY=:0.0 xset dpms force on

or

DISPLAY=:0.0 xrandr --output DVI-0 --off
DISPLAY=:0.0 xrandr --output DVI-0 --auto