Someone please tell me how to remove the BIOS password from my laptop Dell Inspiron N3420

You can remove the battery in the motherboard and place it aggain that will solve the problem ...

@Stefan_1 This is not necessarily true. Usually, the hashed password is stored in non-volatile flash memory. Kabir will probably have to remove the keyboard cover and short out a couple of pins (not sure which) in order to reset the system to factory settings and erase the flash memory where these configuration settings are usually stored. My advice is to go to the Dell web site and in their support section you can start a chat with their technicians who will probably be able to advise you appropriately.

We had this problem with a Toshiba tablet/laptop that my attorney gave us and my grandson had to apply this technique. In less than an hour, he had the BIOS unlocked and Windows 7 installed... :-)