I got a TL-SG108E today to replace an old, non-managed Netgear switch and it's behaving very weirdly.

The setup is as follows; I have a single network cable running from the 3rd floor down to the fuse box where it is connected to the modem. On the 3rd floor I have the switch, a wifi AP and 4 network cables that go to various rooms. One of those cables goes to my work space and when I plug it into the new switch, it doesn't do anything. When I connect to the wifi (also on the switch), I can see in the switch's management page that the "link is down". When I try to do a cable test, it comes out as "open & short" at 0 or 1 meters.

I've tried plugging the cable into other ports; same problem. I've plugged other cables, like the one going to the wifi AP, into the same port and that works perfectly fine.

The weird thing is that, using the older switch, I get gigabit speeds without any problems. And if I plug the same cable into the wall directly (connecting it straight to the modem), it also works. So it seems very unlikely that something is wrong with the cable and it's clear that the ports on the switch are functioning fine with other devices attached.

Is this some sort of bizarre incompability between switch and cable? Is the switch somehow broken? I also cable-tested the cable just to be sure and there are definitely no shorts.

On another note; one of the cables going to another room that has a PC attached to it will auto-negotiate 100mbps, even though the device can handle 1gbps. That issue also did not occur with the previous switch.

What is going on here?