I have dell latitude d420

Need master code to reset the bios.

Service tag ;#3XLVP1S-595B

I can't boot from any cd,usb,hard drive.

Help me.

Here's a link to a site where you can download "CmosPwd". It's free. It claims to be able to determine master passwords on machines such as yours. I haven't tried it so I can't vouch for it.

CmosPwd - CGSecurity (http://www.cgsecurity.org/wiki/CmosPwd)

In the past, we used to simply remove the CMOS battery or disconnect it from the computer (often a jumper) and short the CMOS connections (also a jumper) to reset the CMOS memory back to its default. The usual default is no password. This may still be able to be done if CmosPwd doesn't work.

Get a master password at http://bios-unlock.com/http://bios-unlock.com/
Most dells use the service tag to generate a bios password.