The logon passward has nothing to do with accessing the disk at this point.
Your problems has to do with permissions and ownership.
Since you did not specify Operating System or File System the assumption here is that you are using an NTFS based file system and hopefully as Dee-dhn pointed out, EFS was not employed. If my assumptions are incorrect then I apologize and you may disregard this post.
You must take ownership of the drive in order to access the files and folders on it. By default ownership is inherent to the original user.
First you need to disable Simple File Sharing if it is not already:
My Computer -> Tools -> Folder Options -> View tab -> Scroll to the bottom of the list of advanced settings and un-check Use Simple File Sharing (Recommended) -> Click OK.
Next go to the folder and right click on it and select Properties -> Security tab -> Advanced button -> Owner tab.
Select a new owner from the list and put a check in Replace owner on sub containers and objects -> Ok -> Ok