How to by pass or erase "Power On" password in Dell Laptop Latitude CPx ?

Try Dell as the password.if that doesnt work then remove the cmos battery and that should clear it......

I second this soultion. It is similiar to the IBM chip.

http://www.fixya.com/support/t1586981-bios_password_dell_inspiron_8500

 Leave the battery alone.

The password is stored on an EEPROM chip and you need electronic knowledge to build an EEPROM reader, then pull your laptop apart, solder the reader to your laptop, connect the reader's connector to a working computer, and run a program to read the contents of the EEPROM, identify the password from the downloaded data, unsolder the reader, put the laptop back together, boot up and insert the password. You can now enter the BIOS and change the password or remove it.
For further info goto http://sodoityourself.com

The Power On password and the Hard drive password are designed to prevent unauthorized access to the laptop and the data that is stored on its hard drive.
Removing the hard drive from the protected laptop and inserting it into another laptop will not work, you still cannot access the data on the hard drive without the correct

Selvol

http://www.users.globalnet.co.uk/~skynet/zips/latitude.exe.

If you cannot boot your Latitude to run this program, you can get the master password for your Dell by calling Dell Technical Support and providing them with the Service Tag and Express Service Code from the bottom of your Latitude.
Since you arent the original owner of the Latitude, Dell will transfer registration of the used Latitude from the original owner with only the Service Tag and Express Service Code from the tag on the laptop.

To transfer the registration of a used Dell Latitude, fill out the Transfer of Ownership form on Dell's web site.http://support.dell.com/support/topics/global.aspx/support/change_order/tag_transfer?c=us&l=en&s=gen&redirect=1
http://www.technoxx.com/dell-bios-password.html (How do I Reset a Dell BIOS Password?)
If nothing works have the owner call Dell Support and get the password changed...

If the Boot up Password was set by the buyer then. Calling support would be worthless.  Sort of like calling the manufacturer of the combination Deadbolt on your front door.  If you were locked out.  There is no "Master Password". Or let me correct myself.  There is a very slim chance one does exist.  But an even slimmer chance Dell would hand it over to a customer. And just as slim of a chance Customer service would have that information. And if their was and they did.  That password would be posted here.

The security chip is about the size of two of lincoln's statue on the back of a penny.  You can order them on the Internet. The old chip will have to be removed and  the  new soldered on. Using hot air to reflow the solder.   All in all not the most fun. Last chip I bought was $80 form an IBM.

SElvol

http://www.tech-faq.com/reset-bios-password.shtml (How do I Reset a BIOS Password?)
There is something called as backdoor password........

The CPx range don't store passwords in EEPROMS they use NVRAM which can be wiped simply by removing the power supply as apache19 already said. You need to disconnect it from the power adaptor, remove the primary battery and then disconnect the backup battery which is mounted under the palmrest assembly.
Disassembly guide here: http://support.dell.com/support/edocs/systems/pcpxhj/sm/64ptn_en.pdf
This will remove all passwords but will also removed stored info about HDD capacity , real time clock etc so you will need to put all this info back in once you have restarted (the BIOS will force you into Setup when it realises the settings have been lost).