history disappears after restarting computer

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 in "History". Move those files, and only those, to the Desktop, leaving the window open. Relaunch the application and test. If there's no change, quit again and put the files you moved back where they were, overwriting the ones that may have been created in their place. Otherwise, delete the files you moved. The browser history will be empty. If possible, restore the deleted files 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 won't see what you pasted because a line break is included. Press return.