If you google it you find the common issues are expired antivirus, incorrect date and time and trojans. It's rarely something else.
Tell more.
Suddenly the computer is not able to connect to internet, sometimes I can connect to router, but never to actual webpages. On the phone and other PC, internet is working fine. If Ethernet cable is connected, it shows unidentified network. If wifi - connected, no internet.
Just spent 4 hours trying various tips like: win - CMD - ipconfig release and renew, which both bring up errors, DNS change to automatic or 8888/8844. Uninstalling adapter in device manager and scanning for changes, nothing helped yet. Also did a factory reset on router.
Thanks for the help.

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