Q: Safari history keeps deleting

Make a "Genius" appointment at an Apple Store, or go to another authorized service provider. You may have to leave the machine there for several days.

Back up all data on the internal drive(s) before you hand over your computer to anyone. There are ways to back up a computer that isn't fully functional—ask if you need guidance.

If privacy is a concern, erase the data partition(s) with the option to write zeros* (do this only if you have at least two complete, independent backups, and you know how to restore to an empty drive from any of them.) Don’t erase the recovery partition, if present.

Keep your confidential data secure during hardware repair.

Apple recommends that you deauthorize a device in the iTunes Store before having it serviced.

*An SSD doesn't need to be zeroed.

When you use Private Browsing windows, Safari doesn’t save your browsing history, and it asks websites you visit not to track you.

Do a backup, using either Time Machine or a cloning program, to ensure files/data can be recovered. Two backups are better than one.

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

I don't remember posting that comment, and I must have done so by mistake. Obviously it has nothing to do with the question.

Please back up all data before proceeding.

Triple-click anywhere in the line below on this page to select it:

~/Library/Safari

Right-click or control-click the line and select

          Services ▹ Open

from the contextual menu.* A folder named "Safari" should open. Quit Safari if it's running. One or more files in the open folder should have a name beginning as follows:

          History.db-wal

Move those files, and only those, to the Trash, leaving the window open. Relaunch the application and test. If there's no change, quit again and move any other files with a name beginning in "History" from the Safari folder to the Trash. The browser history will be empty. If possible, restore the file named "History.db" from a backup that predates the problem.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination  command-C. In the Finder, select

          Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You may not see what you pasted because a line break is included. Press return.