nukemaster :
You need to take ownership of it.
Since the OP didn't follow up, I wanted to say I had the same problem and nukemaster's fix worked perfectly. Thank you!!!
In my case I had data partitions on a separate drive, let's call it disk 2. I did a clean install of Windows 7 on disk 1, and subsequently one of the four partitions on disk 2 was not accessible. (Of course this was the one I most urgently needed.)
Disk Manager showed the troublesome partition had its proper label and drive letter, it was healthy, it contained data, and an error check showed it was in perfect shape. The partition was visible in Windows Explorer but was not accessible at all.
Nukemaster's insight into the permissions was spot-on. For some reason this partition was set up long ago with "me" as the owner. By "me" I mean my old profile from Windows XP. The other partitions on that disk showed the Administrators group to be the owner.
Taking ownership of the partition and all subfolders allowed me to get access to my data once again.