This could be caused by Data Corruption, as a last resort try a different cable, different computer and a different cable, If this does not help you might need to click the following links to use a Data Recovery Software or Company to extract the data.
Something like TestDisk http://www.cgsecurity.org/wiki/TestDisk may fix the problem. Read through the tutorials first. If you only have one copy you don’t have a backup.
I tried hooking it up to my laptop and all my data is there. But it keeps telling me I need permission. The original problem is, I screwed up the permissions under the security tab and I am not sure what to do