Slow internet on Windows PC

I’ve just rebuilt an old PC I had here to sell to a friend. I’ve installed for him a Window 10 Pro. But the internet speed is being unusable.

Regardless of wired ethernet or wireless adaptor, speed is around 1Mbps at best, and downloads are between 20 - 40kb/s.

I’m not familiar with Windows. Is there something I am missing? My other computers on the same network, one using this same ethernet cable, are just fine at 16 - 20 Mbps.
Is there a bios setting or motherboard driver needed for windows?

The m/board is an ASRock H87 Performance. I last used it about one year ago when I updated to Ryzen, and it’s never had network problems before.

Given that you have tried the same cable on a different computer and the speed was fine, it is probably a windows config error.

Try downloading the latest ethernet driver from ASRock’s site, install it and reboot. Another thing to check is the link speed, that is under control panel> network connections> right click settings of wired connection(may be called something else). If you are at say 10Mbps then that is your issue, you can manually set the link speed in the same window.

Thanks for that advice.
None of those solved the issue. However I have found that, whilst testing the computer during the week, this issue goesaway after about 15 minutes (speed test shows 14Mbps, and downloads go to 1.8mb/s).

This is consistent everytime I turn this PC on, and applies to both wired connection and usb3 wireless adaptor.

I don’t know shit about windows. I can only assume windiw 10 Pro takes a while to start some internet related service.

Windows 10 is terrible about running stuff in the background especially at startup. Could even been windows update hogging bandwidth. Did it happen to show high network usage in task manager after boot? Something easy to check that’ll tell you real quick if something else is using bandwidth or if it is a config issue. Running a DNS flush a winsock reset couldn’t hurt either even though it is a fresh install. Is it already updated to 1803?