Hi,
In the first place Dell will not give you a password to unlock computer unless you prove to them you bought the computer ...your address..and your date of purchase.
Try to reset the CMOS.
disconnect the computer from the mains supply, open the casing, remove the CMOS battery.
reset the CMOS by using the jumper, replace the jumper to its original position, put back the battery and start the system.
If It is NOT possible to reset a Bios password just by removing the cmos battery you will need professional assistance.
unlock the Dell password with Service tag termination in
http://www.laptoprebirth.com
Thank you