Default Ethernet cable no longer working?

From reading this thread, it seems you have a combination of problems, not the least of which is tampering. You may have an intermittent connection due to the router / switch failing. You also might have someone monkeying where they have no business monkeying.

I'd ask the property owner to have an expert, not an amateur, go in and fix things proper, then put it all behind a locked door. You might be asked to share the cost of doing this, but it's probably worth it to put an end to the frustration.

Just one man's opinion.

Doc Brown, how do you keep your server room so neat ???

Okay right now my wired internet doesn't work at all again. I went and took a look and ethernet is plugged into router just like it was yesterday.

Yesterday my wired connection was working perfectly fine.

None of this makes sense now.