Font awesome symbols replaced by squares?

Good morning,

I’ve lost all my font awesome symbols; the menu drop-down list arrows, search bar magnifying glass, etc. I had changed the folder icon (fa-folder) to a star, but thats gone too; all replaced by squares.

I’d be very grateful if someone could explain what I’ve done to make this happen or how to correct it.

*As a note: I haven’t made any changes to the theme or installed new plugins, though I had recently been trying to make the site more secure, such as password protecting admin.

Many thanks.