Ethernet Connection flawed

Hello!

I'm not too sure how long I have this problem, could be a week or a month.

Anyways. On my main system I'm connected to the internet via Ethernet. The cable is pretty long but is directly connected to my router. I have a 100down, 5up package over cable and haven't run into any issues to date (3+years). Only in the past couple of days (weeks?) I noticed my speed going down significantly. Before I reached speeds anywhere from 92-103MBps, now I'm at mere 9. Upload's fine though.

Upon further inspection I noticed that my connection is "set" at 10,0MBit/s (Screenshot) so I updated my Ethernet driver directly from MSI's webpage, still the problem persists. Rolled back the driver, same thing.

I also went into the drivers configuration and tried editing the "Speed&Duplex" setting. None of the settings would end that 10.0MBit/s limit. Screenshot

I reinstalled Windows yesterday and tried the two drivers (the one being MSI's new one, the "old" one the one Windows autoinstalls). Deinstalled the device in the device manager, reboot, nothing. De- and reactivated the LAN-Controller in my BIOS, still nothing. A BIOS update didn't help either.

I could not test different cables because this is the longest I own and have not yet moved my computer next to the router. On my laptop I get full speed (98down, 4.8up) with the same cable though.

Booting into ubuntu from a live USB I couldn't even connect to the internet.

As of now I think my mainboard might be faulty, which would be bothersome but replaceable.

If anyone has more ideas on what to try (other than trying different cables, will do that tommorrow), I'd really appreciate that.

My system:

• CPU: Xeon 1230v3

• Board: MSI H87-G41

• 8GB RAM

• GPU: R9 280X

• Windows 10 Pro64 build 14393.0

Thanks in advance!