Hi Giorgos,
My name is Cindy. I am sorry you are having this problem. I know it is really frustrating. I will do my best to help you with this problem.
Let's check the network adapters. They can become corrupted and fail to work.
Please type the word Device Manager in the search and open the page.
Click on the Network adapter folder and open it.
Do you see the Network Driver for your Internet provider? Right click on it and uninstall.
Then restart the computer. Windows will automatically reinstall the driver.
Then check to see if this fixed the problem.
Best Wishes,
Cindy
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