Are you certain the monitor is actually stuck in sleep, and hasn't just switched over to the analog input? (My Acer X223W has this issue sometimes after the display goes into power save mode.) There should be a button or menu on the monitor that allows you to switch the input source. Have you tried power cycling the monitor?
If that isn't it, try powering everything down, unplug all power cords from the wall outlet, and wait 30 seconds. Plug everything back in and try powering the system up.
Nostalgia isn't what it used to be.