Launch Safari with the shift key held down. Then clear History… all history : [Clear History]. That will get rid of all cookies and history. In Safari Preferences : Advanced : [√] Show Develop menu in menu bar. In the Extensions tab, disable all extensions. Close Safari Preferences. Now, you can press option+command+E to clear your Safari browser cache. Quit Safari.
Download and run Malwarebytes for Mac to see if it finds any browser hijacking malware. Any malware that it finds, it will offer to remove.
Now, launch Safari normally. Does it still hang?
Disclaimer: Although I personally use Malwarebytes, I receive no benefit from the vendor for mentioning their product in the support communities.