Hi, I had the same problem and
joey2007ua was right, it was something to do with the graphics
drivers.
Although, I was using HDMI instead of DVI.
Just to point out to anyone having this issue, you will need to re-install Windows 7 once you connect the PC via VGA, as it came up with a "Windows setup encountered an error..." when I switched the cable from HDMI -> VGA and just restarted.
I haven't tried to get the HDMI working yet, but I assume it will just need the new
drivers and then I can switch the cables, but at least I'm actually in Win 7 now!!
Cheers