Q: Cannot Connect to Internet : This site can’t be reached

Adware may be  installed on your Mac. Remove Adware.

1. Use  Malwarebytes Anti-Malware for Mac to remove adware.

     https://www.malwarebytes.org/antimalware/mac/

   Download, install , open,  and run it by clicking “Scan for Adware” button   to remove adware.

   Once done, quit Malwarebytes Anti-Malware.

2. Disable Extensions and test.

   Safari > Preferences > Extensions

   Select and disable all extensions and test.

   Enable Extensions one by one and test.

   To uninstall any extension, select it and click the “Uninstall” button.

3. Safari > Preferences > Search > Search engine:

     Select your preferred search engine

4.  Visit the site you want it to be the Home page

     Safari > Preferences > General >  Homepage

     Click the button “Set to Current Page” button.

If the answer posted above doesn't help:

You will have t do this after starting up in Safe Mode to prevent adware

from interfering with the removal of adware .

1. Shut down the computer.

    Press the power button. Immediately after you hear the startup sound,

    press and hold the Shift key.

    The Shift key should be pressed as soon as possible after startup,

    but not before the startup sound.

    Release the Shift key when you see the Apple logo on the screen.

    Startup will take longer than usual.

    Screen flickering is normal in Safe Mode.

    Login to your account. Launch Safari.

    Enter this address       https://www.malwarebytes.org/antimalware/mac/

    in the Safari address bar.

    Download,   Install , open,  and run it by clicking “Scan”  button   to remove adware, if present.

    Once done, quit MalwareBytes.

2. Safari > Preferences > Extensions

    Turn all extensions off

     or  uninstall all extensions you haven’t installed knowingly.

3. Safari > Preferences >  Search > Search Engine :

    Select your preferred   search engine.

4. Safari > Preferences > General > Homepage:

     Set your Homepage.

5. Restart normally using the “Restart” button.