Go step by step and test.
1. Click in the menu bar and choose “Force Quit”.
If Safari shows up on the list, select it, and then click “Force Quit” button.
Hold the shift key down and launch Safari.
2. If Safari is slow, stops responding, quits unexpectedly, or has other issues
Safari > Preferences > Extensions
Select and turn off all extensions.
Section: Manage Extensions
3. If you can’t open a website in Safari
4. Safari > Preferences > Advanced > Accessibility:
Uncheck the box beside “Never use font sizes smaller than”.
5. Delete com.apple.Safari.plist file and test.
Empty the Trash.
Quit all applications.
Hold the option key down and click the "Go" menu in the Finder menu bar.
Select "Library" from the drop down.
Library > Preferences > com.apple.Safari.plist
Right click on it and select "Move it to Trash".
Restart and relaunch Safari holding the shift key down.
If this doesn’t help, “Put Back” the com.apple.Safari.plist
Right click on the Trash icon in the Dock and select “Open”.
Right click on the com.apple.Safari.plist and select “Put Back”.
Select ”Replace” from the dialog when it appears.