You come to a gym computer that has a message that says "Check Signal Cable" how do I fix this?
Very easily!
This message is informing you that monitor is on a different source. Much like a TV at your home the monitor has multiple sources.
Here are the steps.
Monitor looks this.
You need to press the select button and change the source. Where is the select button? See picture:
After you change the source the monitor should boot up and look like this.
After it is on this screen in a couple of seconds it will connect to your desktop.