Great ethics question. At least two variables:

* Can the owner be found?

* Does the owner have control of another copy?

The second question makes the rationalization harder: "Aw, shucks, no way I can find the owner, and no sense letting BTC go to waste."

If the computer was discarded, I wouldn't consider it stealing. However would I feel like I had a duty to return it to it's previous owner or heirs? It depends on the circumstances. I have not taken/stolen significant sums of money in the past for moral reasons.

I don't think your comment should have been downvoted as it is thought-provoking, but it might have been downvoted since I said "discarded", and thus taking it wouldn't be stealing.