Yasou!
You said the mouse is jerky and the screen flickers. Sounds like a battery leakage issue. Check the battery for leakage. Also remove the old battery if it is still there and replace with NiMh or Lithium (with hack on aminet) If there is some corrosion clean it with Isoprepal Alchohol and old toothbrush! The Amber circuitry is near the battery and it sounds like it has been corroded!