Are you trying to use the motherboard-integrated video card's vga slot? Maybe it was set to disabled in BIOS. In that case, I'm not sure if it helps, but you can try to remove the video card. Maybe you'll have to borrow a DVI monitor from a friend for checking out BIOS settings.
You can get a DVI-I to VGA adapter, they're very cheap. Since it doesn't convert any signals (DVI ports support both analogue and digital signalling natively, just one at a time) it doesn't have any problems like some adapters/converters do.