A computer us a tool to accomplish something. What does he want accomplished? Find something in his life that interests him, do something cool with the computer to related to his other interest.

Maybe is collecting something. Work with him to take digital pictures of each of the items in his collection and put them on the computer. Are there more items that would fit in his collection that he doesn't have? Make a map of those other things/places. Make a wishlist of outstanding collectables consumable by grandparents that are looking for gift ideas.

The computer shouldn't be the goal. What can be done with the computer to make your life better (however you define that) should be.