Bear in mind that none of these tools can look into directories where the administrator account (yes, there are places Admin can't look) does not have permissions. One example is the hidden "System Volume Information" directory, where your system restore points are stored. Only the "System" account has permissions there and it will always show 0 bytes to all others, even when there are several GB stored in there. And I wouldn't go messing around with permissions on any of those locations unless you have verified backups at the ready.