It's a setting on your monitor and not your computer. Go into the monitor's OSD menu and select Input, then select DVI (or whatever your main input is). Just make sure your computer is on and providing a video signal to the monitor. If manually setting the input does not work, try unplugging your monitor for 30 seconds and then plug it back in to see if that resets the monitor input interface to "Auto Detect". Also, check the physical connection of the cable going into the monitor as well as the connector going to your video card.
I tried this, though there was no option to select an input, though I remember in the change screen resolution screen, there used to be additional options as opposed to simply vga.