unusual windows problem

After going to bed a couple of days back (I leave this system on 24/7) I turned my monitor on, waved the mouse around to wake up the display, nothing happened so I reset. Same think happened after leaving it alone for the same amount of time the next day, so I turned the display power saving mode off. Woke up again and this time I got my desktop etc for a few seconds, then it shut off the display. Nothing looked out of the ordinary.

I'm trying another video card, but it doesn't seem like I'll know whether the fault has gone until I go to bed and wake up again, so I'm just posting to see if anyone has heard of something like this? There was nothing unusual in the app or system logs. Also, I haven't been coming back to the computer at the same time, it's been several hours difference each time.

When did the issues start? Is this a new system? What changed around the time the problems started (the answer is almost never "nothing")?

Here is what I would start with:
1) Make sure the monitor isn't having issues. One of my screens will go to sleep and will randomly not wake up until it is hard power-cycled (caps are likely going out).
2) Make sure the USB controller isn't being powered down by Windows.
3) See if you can remote in from another computer or ping from another system.