How can stolen items and what has been consumed of them be returned without the thief being discovered, given that one of the main stolen items (the computer) is out of order?

Whatever remains of the stolen goods should be returned as is. For what has been consumed or damaged, its value should be returned as of the day of the theft, not the day of return. As for what he has forgotten or become confused about, he should strive to estimate it until he is reasonably certain that what he will return covers the value of all that was stolen.