LG Monitor - Connecting Two Computers

The monitor likely switches the video input electronically when it detects a connection from either the digital (DVI-D) or analog (D-sub) connectors. If you connect two different running systems simultaneously, one to each video input connection, you could likely blow the monitor or get the blank screen that you've observed. You're probably lucky you didn't blow the monitor without checking with LG tech support first to determine if your model supports this arrangement.

Some monitors may be able to handle two simultaneous connections, but would give priority to either the digital or analog connection unless there was a way to manually switch from the monitor's control panel. This is a very model specific question and depends on the design of your particular monitor.

You should contact LG Electronics tech support and ask this question. I think they'll tell you not to do it or you'll void your warranty. You could also download the product manual from the LG website.

Regards

I was doing exactly what you want with my Dell monitors a while back. One PC on DVI, and the other on VGA. There was an input switch on the bottom of the monitor. Pressing it toggled from one input to the next.
You might start by going through all of your monitor's settings to see if you can find it.

EDIT:
Should work:

Glad you got it working!