Hi Edwin. I'm Greg, a Volunteer Moderator and 10 years Windows MVP here to help you.
I'll give you everything possible for Ethernet problems to try so that hopefully something works:
Right click the network icon in System Tray at bottom right end of task bar to Troubleshoot Problems. Choose "I'm having a different problem" and then "Troubleshoot Network adapter."
Try powering off modem, router and PC and then restarting in that order with 1 minute in between each.
Try all of these steps:
https://support.microsoft.com/en-US/help/10741/...
https://www.kapilarya.com/how-to-reset-network-...
https://www.pcworld.com/article/2835564/when-yo...
https://helpdeskgeek.com/help-desk/8-troublesho...
https://windowsreport.com/fix-slow-lan-speed-pc/ (Avoid ad links which intrude into editorial copy, especially avoid Restoro ad)
https://www.onecomputerguy.com/why-is-my-ethern...
Update your network adapter drivers from the PC maker's Support Downloads web page using the full model number, HP Serial Number or Dell Service Tag on sticker. Compare the latest drivers available for download with the ones presently installed in Device Manager reached by right clicking the Start Menu. Make sure you have the latest BIOS or UEFI firmware, Chipset, Display (Video), Sound, USB3, Bluetooth, Network and all other drivers, or else download and install the latest now.
If you have the latest network driver then try on it's Driver tab also to Roll Back, or Uninstall and then restart PC to reinstall the driver. Try also all older drivers from Update Driver > Browse > Let Me Pick list working backwards.
Go to Device Manager > Network Adapters, select Ethernet adapter, then Power Management tab, clear the check box to "Allow the computer to turn off the device to save energy." Then on the Advanced tab disable any energy-saving options.
If this was caused by Windows Updates then you can check which were installed at Settings>Update & Security>Windows Update under Installed Updates, then uninstall them from the link there, and hide with the Hide Updates tool:
https://www.howtogeek.com/223864/how-to-uninsta...
You can also use System Restore to get before the problem began, then check for Updates with the Hide Update tool and hide them:
https://www.windowscentral.com/how-use-system-r...
If this was caused by Version update then you can roll it back in Settings>Update & Security>Recovery and then hide it until it matures using the Hide Updates Tool:
https://www.howtogeek.com/223864/how-to-uninsta...
Right click the network icon in System Tray at bottom right end of task bar to Troubleshoot Problems.
If you're plugging into a router then try plugging into the modem directly. Try turning off Modem and PC, wait 15 minutes to turn back on the modem, then the PC.
You also are entitled to Support from your internet provider to get online on all devices. This is always included in the monthly bill. If your router is less than a year old they will also Support getting it connected and optimized.
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.
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