A user with a similar problem had posted that they used the password admin and it worked, though that could have been pure luck. In general though to access the BIOS you will have to call Dell tech support and after confirming you are the owner of the system, will help you access the BIOS.

Welcome to the Dell Community @nishant1998 

Dell Support for lost BIOS password:

https://www.dell.com/support/article/us/en/04/sln314479/dell-support-for-lost-bios-password?lang=en

Dell System prompts for a Hard Drive (HDD) or BIOS password:

https://www.dell.com/support/article/us/en/04/sln142655/dell-system-prompts-for-a-hard-drive-hdd-or-...

Best regards,

U2

https://biospassword.eu/dell-free-passwords

https://bios-pw.org/

http://dogber1.blogspot.com/2009/05/table-of-reverse-engineered-bios.html

What do you mean by format my windows? Reinstall windows or format a drive or what? Explain exactly what you want to do before doing anything. You must be signed in as an Administrator to make changes. If you are using a Local Account, reboot the computer and sign in to the Administrator account.

when i tried to boot my pc from a usb drive it asks for the bios password. without bios password i am not able to sign in as administrator

biospassword.eu is a scam.  I provided them with my asset t ag number and they gave me a passcode that did not work. When I asked them for a refund they stopped responding to my emails. I started a fraud claim against them on PayPal. 

If you don't know the BIOS password, you are out of luck.

I also have a problem of password authentication system. On Google (bios password.eu/dell-free-passwords) they say [under construction] so how am I going to solve that. Thanks