A little confused here...
Your subject states the files are not visible on the hard drive, but you state in your post, the files can be seen but are not accessible. Is this the case?
Has this drive always been in the computer you are referring to? Can you access any of the files at all? Have there been any changes to the "Users" permissions on this computer? Are any of the files on it private?
Try this:
1. Boot into Safe Mode.
2. In Windows Explorer for that particular drive go to \Documents and Settings\ and right click on the username folder.
3. Check the Security for the folders for that particular user and make sure the files and folders are not set as private.
See if this works, at all, and post back with your results...