No tengo el password de BIOS del latitude e5400

BIOS passwords on Dell laptops cannot be recovered. If you have forgotten one of the passwords that is set in the BIOS, contact Dell Technical Support to obtain a password release code. The password release code is based on the unique password prompt that is generated using information from your Dell laptop.

Be prepare to provide ownership information.  If the system is out of warranty, there will be a service charge.

You should contact the seller to unlock the password and to provide information for your ownership transfer request.  Otherwise, return the product for a refund.  In warranty or not, Dell support won't be able to assist you if you are not a registered owner.