Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, bear with use; post back with a clear picture of the "...black circle on screen of camera..."
Still, the described symptom almost always point to an internal hardware issue or more particularly, possible fault with the LCD screen itself.
This would require that the unit be opened up for visual inspection, voltage/continuity/resistance checks, confirm faults and effect repairs.
If comfortably able and feel safe to do so, are you then considering a DIY (do-it-yourself) repair approach? If yes, please click HERE for a potential source of replacement LCD screen.