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Press Command, Option and Esc keys and this will bring Force Quit window. Select Safari and click Force Quit. This will close Safari.
Then hold down Shift key on your keyboard and open Safari. Click on Safari menu and select Clear History and Websiate Data. Select All History and click Clear History. (For older Safari, you will see Reset Safari. Click it and reset Safari)
Please let me know if that didn't work, so we can continue troubleshooting