Good, that means you have a good video connection to the monitor. Now we need to figure out the connection from the Win 7 PC to the KVM, it seems.Forgot to mention the windows 10 PC is showing up on the monitor using the HDMI output on the switch conected to DMI port on monitor.
What video ports does your Win 7 rig have? How is it connected to the KVM?
Then I assume you have the HDMI to DVI cable connected to the monitor. Is that correct?