The monitor presence detection seems to be working. If you set the nVidia mode to Clone, you should be able to see the desktop on either connection.

If this doesn't happen, any chance of temporarily connecting the monitor to another system with DVI? If it behaved the same way, it would suggest a faulty DVI input on the monitor. I can't say for certain if there's any type of cable fault that could allow monitor detection but not supply any signal, but being digital I doubt it.