RE: Password protected hard disk. How to unlock it?
This is a two-dimensional issue - there's the system (BIOS) portion of the password. To have that cleared, you'll need to call Dell support with verification of ownership.
This will not, however remove the password from the drive. The cheapest solution is that once the CMOS portion is clear, to replace the drive with a new one.
If you need to have the password removed from the drive to access the data on it, you'll need to send the drive to a recovery service with the tools to do that job -- it will cost more than a replacement drive by at least a factor of about four, so if you don't need the data, simply replace the drive.