There are two parts: The password is set in EEPROM on the mainboard.  You'll need to call (voice) Dell support and verify your system ownership to have that removed. This will not remove the password from the drive, however;  lost passwords cannot be user-removed.   If you do not need the data on the drive, once the EEPROM is clear, cheapest option:  replace the drive with a new one. If you DO need the data on the drive, contact a data recovery service that has the tools to access the user-inaccessible portion of the drive and remove the password from it. DO NOT install another drive until the EEPROM is cleared.  If you do, the replacement drive will inherit the unknown password.  
i forgot my HDD password How do I get it
HDD password