This is a harder variant of the following question: Three boxes, Four questions, Three times not true, Once the truth
The difference is that now there are four (not three) boxes, one of which contains a treasure. The rest is the same: You can ask exactly four yes/no questions, and the guardian will answer exactly one of them truthfully, and the other three falsely. Afterwards you open one box, the other three disappear, and you get the treasure if it was in the box you opened.
You can't ask about future events, the guardian's not psychic. Forcing the guardian to answer with a truth value ("Will you answer this question negatively?") will cause his head to explode, forfeiting your remaining questions.
How can you ensure you open the box with the treasure inside?