The monitor isn't waking up because it isn't being sent a signal from the graphics card. Most likely, it is a Windows driver problem with the graphics card, or other than that could be a graphics card problem. With a slight possibility of it being the motherboard. Check the Windows Event Viewer to see if it indicates the problem. I suggest updating your graphics card drivers (if possible). If that doesn't work, or you have the latest, try resetting the CMOS, testing that, and if still not working, updating the BIOS.