Question Wired internet drops, other computers on network are fine

Oct 7, 2019
My computer keeps dropping internet (wired): the internet connection says disconnected but then comes back seconds later. This happens several times an hour. Other computers connected (both wired and wireless) to same the router are all fine/stable. Things I've tried:

-A brand new network card
-New ethernet cable
-Using other ports on the router
-Clean install of Windows (W10 Pro)
-Network commands (netsh winsock reset, netsh int ip reset, ipconfig /release, ipconfig /renew, ipconfig /flushdns)
-BIOS update
-Giving the computer a reserved IP on the router

None of these have fixed it.

The computer is a i7-3770K, MSI Z77A-GD65 motherboard, 32gb RAM, OS drive is on an SSD.

If it helps to know this, I'm pretty sure the computer has done this its whole life, but it never mattered (apart from being annoying) when just checking email and browsing. I've started needing to use it for Skype and the intermittent disconnecting means it drops the call, which is a real problem!

At a loss as to what to do. I don't want to scrap the computer, but I really don't know what to try next. Totally out of ideas. Help very much appreciated!