Much shorter, but you need to mention the power issue briefly in your opening sentence. Otherwise, it doesn't make any sense in the second sentence. A short sentence that says while you were in the shop, there was a power outage that resulted in a lot of confusion in the shop area and the cashier, would be helpful.

One other point. I don't think it strengthens your case that you mention that a whole month went by before you noticed the tire missing. I would leave it out and use a more nebulous word. You're trying to get them to help you, and the word 'month' seems like an eternity to me... <img src="/forums/images/graemlins/smile.gif" alt="" />