Dell latitude e6400 #CDG404J-2A7B password authentication system

SOURCE: dell latitude e6500 cmos password

There are 3 ways to do this but the first requires that you provide proof of ownership to Dell, or it will cost you money via other "service" providers on the web or you can do it yourself - for free. Now, "free" and "easy" are two different things.. but if you can carefully open your notebook without damaging it - here's a couple links from Dell that detail the CMOS battery removal process:

http://support.dell.com/support/edocs/systems/late6500/en/sm/html/coinbatt.htm

and

http://support.dell.com/support/edocs/systems/late6500/en/sm/html/coinbatt.htm

The key is to disconnect the AC power and main battery before dis-assembly and then then disconnect the CMOS battery as shown in the links above. Press and hold the power button for a minute to completely discharge any power in the main board components. When you remove all the power from the PC, the CMOS can not maintain the customized BIOS settings, including any password settings. You have in effect, reset all settings to "Default". Reassemble when done.

The PC will need to have the BIOS settings set again - to your liking upon next boot.

I hope this helps!