How to test/reactivate the DVI port of a monitor?

How to test/reactivate the DVI port of a monitor?

One of my monitors seems to have a "broken" DVI-Port with some strange
behaviour:
VGA works fine
When plugging it in DVI, the nvidia-settings tool finds the monitor and
the correct Hardware-Details, and i can configure the Monitor settings.
After applying the settings the monitor switches between powersave mode
and activating (without anything on display) back and forth.
i tried different resolutions and refresh rates, which work fine on VGA,
with the same result.
Can a DVI Port break, with VGA still working?
Wouldn't the monitor disappear from the nvidia-settings tool, when te port
is really broken?
The DVI-Port of the graphics card is working just fine with other
monitors, i tried the HDMI-Port with a HDMI->DVI cable which works with
other monitors, but did not work with this one either.
The monitor is a "Medion MD30919PO S09".