The X-Ray tab should show greyed out if the book does not have it or if the specific word accessed is not in it. If your device does not have a wireless connection, the Wikipedia tab will be greyed out as well.
If you did a device reset, then you will have to call CS to request an exchange.
You may want to download the latest firmware version from the Amazon site and try to reinstall it. If you damaged the firmware you have, a re-install may fix it.
Here is where to get it:
http://www.amazon.com/gp/help/custom...deId=200529680