If you have not done this already, go step by step and test.
1. Startup in Safe Mode and restart normally using the “Restart” button at the bottom.
https://support.apple.com/kb/PH25617?locale=en_US&viewlocale=en_US
2. Delete Caches and test.
Close all windows and quit all applications.
Hold "option" key down and click "Go" menu in the Finder menu bar.
Select "Library" from the dropdown.
Library > Caches > com.apple.Safari
Right click the com.apple.Safari file and select "Move To Trash.
Close windows and relaunch Safari.
3. Delete com.apple.Safari.plist file and test.
Backup the Mac.
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. Click “Start using Safari” link at the bottom.
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.
4. Uninstall any anti-virus software, if installed.