You need to take ownership of the folders and file on that drive. They ownership & permissions are currently set to your old Windows Operating System's Administrator account.
To do this, you need to log into the Administrator account. If you're using Home Edition, you need to boot into safe mode in order to gain access to the admin account.
You then need to go to My Computer, then right click the drive in question, click properties, select the security tab, advanced button, then set ownership of the drive to the current Administrator account.
Instructions available in the following guides: