I agree that if you could prove that (if not(provable(P)) then provable(P)), then you could prove provable(P). That being said, I don't think that you can actually prove (if not(provable(P)) then provable(P)). A few times in this thread, I've shown what I think the problem is with your attempted proof - the second half of step 3 does not follow from the first half. You are assuming X, proving Y, then concluding provable(Y), which is false, because X itself might not have been provable. I am really tired of this thread, and will no longer comment.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.