You get into VGA mode by pressing F8 during boot and choosing it from the menu (it will still output via the DVI connector). But, if you're not getting that far that's not going to work. I'm beginning to wonder if your video card has a hardware fault; I'm not aware of anything else that would cause a reboot without even trying to boot Windows.
You could always remove the video card, boot, remove the drivers, shutdown and put the card back in to see what happens.
The Video Card works fine with XP. Could it still be faulty hardware? I've never had any problems with it.