This is not the solution to the problem. But I have also experience such a few times myself. My temporary fix is just turn the monitor off then back on again instead of rebooting. Just an idea.
After going into sleep mode, the monitor remains in sleep after moving the mouse or typing on the keyboard.
My video card drivers are updated.
I plan to turn off sleep/hibernate in power options, but I'd like to know the cause of this problem anyway..
Anyone have any ideas?
Nvidia 5900 ultra
Compaq 15" LCD