I suggest that you contact support -
How to reach support (FAQ) - http://forums.microsoft.com/WindowsOneCare/ShowPost.aspx?PostID=2421771&SiteID=2
If you can provide a clear digital image (photo or scan) of the key, support can help decipher it if a magnifying glass does not help.
Alternatively, exchange the retail copy for another at the store you purchased from since the product is useless unless you can activate with the key. They should honor the exchange.
-steve