I think you need to run the GEForce wizard, it happened with mine. However my pc totally locked on me and on re-boot went into chkdisk mode, after that sequence had run and the pc booted the wizard popped up all by itself telling me that it had found new hardware. I ran the wizard and now the monitor accepts the DVI cable and the VGA cable, I tried both after the wizard had run. Using the DVI cable with no problem now.
Sorry I can not be more helpful than that.