If the password is logon password for Windows OS, you can reset the password with a password reset disk.
See: [http://www.password-buster.com/resource/reset-dell-laptop-password.html|How to Reset Dell Laptop Password?]
If the password is BIOS password, you need to remove the CMOS battery.
See: [http://www.password-buster.com/resource/how-to-reset-or-remove-bios-password.html|How to Reset or Remove BIOS Password?]