Switching

I just started working in a distribution facility with 50+ desktops on the plant floor. My manager is on vacation this week, go figure, and I am tasked to deploy another unit with domain access. I have a need to use an existing connection from the switch that runs to the plant floor. It is right beside another desktop that has domain access, plugged into to a double gang wall plate. Thinking the other port would be hot, I had the desk moved and everything powered on, but I dont get any signal from the other port.

I have a PoE switch that was used in another office, and I think it was plugged into our general network. I want to use this switch here for this purpose. In my training this is a huge no no, as it could cause switching loops, but I know it was used in another office for a similar purpose. Can anyone talk me out of using this PoE switch for this purpose? I would have to find out if the Cisco switches are running STP I would expect, which I could do hopefully by the end of the day.

Help Reddit!