What should we do with a computer that was left for maintenance and its owner has not returned to pick it up or pay for it for over 8 months, and we have no means of contacting him?

It is not permissible to dispose of the device except after despairing of finding its owner. If despair sets in, it can be sold, and the labor cost can be taken from it, with the remainder given as charity on behalf of its owner. If the owner appears, he has the option to approve the charity and receive its reward, or to receive its value. It is permissible to claim back from him what was spent on the device for storage, repair, and transportation. If its owner is unknown, it should be given as guaranteed charity on his behalf, or spent for the benefit of Muslims.