Inteet slows to a halt on one computer when another connects with etheet - otherwise works fine

I've recently moved in with my partner and found that whenever his computer is on my inteet connection slows down to the extent that I can't load webpages, but the moment his is tued off mine works perfectly. It isn't affected by other devices connected wirelessly (we all have phones and laptops connected most of the time), and if I connect my laptop via etheet, same lead same port, it doesn't have the same problem, so seems to just be something with my computer. We're both on Windows 7, my network adapter is Intel(R) Etheet connection I217-V and I'm using firefox. Where I was living before, I was using the same computer and connected with two others all via etheet and we didn't have any problems...I've tried a few things below but no joy so far:

-checked for viruses with AVG - nothing comes up - and also tried using ComboFix after seeing it suggested as a more intensive tool but again no effect

-different etheet cable and switching us around in the ports

-reinstalled the driver for my etheet adapter and tried going back to an earlier version

-Changed the link speed settings to 1.0Gbps Full Duplex, then 100 Mbps Full Duplex and then back to Auto Negotiation. Also been through the diagnostics for the adapter cable and hardware on this tab and all seems fine

-Changed Gigabit Master Slave Mode to Force Master Mode but no change so then back again to Auto Detect

-Had a look for programs like AMD quickstream that I heard others had problems with but haven't found anything

-Reset TCP/IP

I'd be very grateful for any suggestions and sorry if I've missed any vital information or am overlooking anything obvious - just starting to lea about computing so am still very much a novice with most things! Thank you

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