Safari wont open web pages (maybe other browser either)
I found a source of answer that addresses an issue very similar to yours on Apple Support Communities webpage.

Safari won't load after High Sierra upgrade


  
  Log out of your account.
  
  Click  menu in the menu bar > choose “Shut Down”.
  Then press the power button to start the Mac.
  Launch System Preferences.
  
  Look at the bottom of the pane.
  Do you see Trusteer Rapport or Tusteer Endpoint installed?
  If yes, click it and stop it
  or uninstall Trusteer Rapport/Endpoint.
  Do you have Airfoil app installed?
  Deselect Proxies, if selected.
  
  System Preference > Network > Advanced  > Proxies Tab
  Unlock the lock if you have to.
  Under "Select Protocol", uncheck any box that is marked as check.
  Click "OK" then "Apply”.
  Sometimes third party software can cause this sort of problem.
  
  Please run EtreCheck and post the report here.
  Download it, open Downloads folder, click on it to open and select "Open".
  Select a problem from the “Choose a problem” popup menu box, and then “Start EtreCheck” in the dialog.
  Click “Share Report” button in the toolbar, select “Copy to Clipboard”, and then paste it when you reply.