Why can't I access the Hard Disk of my Nokia N91 after power-up?

Your Nokia device most propably cannot detect the Hard Disk because the back cover is not correctly placed or is missing. The back cover contains a magnet that tells to your Nokia device that Hard Disk can be started.Please check that back cover is properly closed. If the back cover is properly closed and you still have this problem please check with e g a paper clip over the little "box" on the inside of the back cover to verify that if the magnet is missing. In this case please contact your nearest Nokia Service Center.