From your informations, the following facts emerge:-
1. Both of you had signed a Partnership Deed in Sept-11
2. Your friend left the partnership one and half years later but the Deed was not cancelled. So on paper atleast,he still remains the partner.
Now, on whose name is that Computer. What does the Cash-memo say. If it is in your name then its your personal property and if doesnt return it, you can file an FIR against him.
But if it is Company's name. Then your have to take legal action against him by sending a legal notice narrating all the facts that he had left the partnership etc.