Safari/Preferences/Advanced - enable the Develop menu, then go there and Empty Caches. Quit/reopen Safari and test. Then try Safari/History/Show History and delete all history items. Quit/reopen Safari and test. You can also try try Safari/Clear History…. The down side is it clears all cookies. Doing this may cause some sites to no longer recognize your computer as one that has visited the web site. Go to Finder and select your user/home folder. With that Finder window as the front window, either select Finder/View/Show View options or go command - J. When the View options opens, check ’Show Library Folder’. That should make your user library folder visible in your user/home folder. Select Library/Caches/com.apple.Safari/Cache.db and move it to the trash.
Go to Safari Preferences/Extensions and turn all extensions off. Test. If okay, turn the extensions on one by one until you figure out what extension is causing the problem.
Safari Corruption See post by Linc Davis
If that doesn't work, try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work. The intent is to see if it is specific to one account or a system wide problem. This account can be deleted later.
Isolating an issue by using another user account
If the problem is still there, try booting into the Safe Mode using your normal account. Disconnect all peripherals except those needed for the test. Shut down the computer and then power it back up after waiting 10 seconds. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the gray Apple icon and a progress bar appear. The boot up is significantly slower than normal. This will reset some caches, forces a directory check, and disables all startup and login items, among other things. When you reboot normally, the initial reboot may be slower than normal. If the system operates normally, there may be 3rd party applications which are causing a problem. Try deleting/disabling the third party applications after a restart by using the application un-installer or by using the developer’s uninstall instructions. For each disable/delete, you will need to restart if you don't do them all at once.
Safe Mode - About El Capitan
also Sierra
Safe Mode Startup – El Capitan. also Sierra
If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. On the screen with Options, please open Options and check the bottom 2 boxes before running. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.
Etrecheck – System Information
