PASSWORD NEEDED FOR DELL INSPIRON 5100

SOURCE: dell 6400 bios password lose

general info about reseting bios passwords:
http://www.tech-faq.com/reset-bios-password.shtml

Hardware workaround For dell laptops:
http://www.tech-faq.com/dell-bios-password.shtml

SOURCE: inspiron 5100 bios a32, keyboard

You can try reseating the keyboard connector. If that doesn’t work, the keyboard needs to be replaced. To reseat the keyboard connector, follow this link: http://support.dell.com/support/edocs/systems/ins5100/en/sm/keyboard.htm#1084976
Be sure to remove AC power and the Battery.

SOURCE: how can i unlock dell latitude d420 bios password

Clearing the CMOS will reset the password...
Take the button cell battery out for a few minutes, put it back in, and all settings, including the password, should go back to defaults.
Unfortunately it looks like your BIOS battery is under the keyboard...
Dell has got what looks like decent directions here, for getting at it:
http://support.dell.com/support/edocs/systems/latd420/en/SM_EN/coinbatt.htm#wp1123951

SOURCE: How to Unlock Dell inspiron 1520 Laptop Password

I is my understanding that you can contact Dell with the service tag, and express code and get the master password to clear forgotten passwords.

SOURCE: Dell inspiron 1300 bios password

A. By Using the Motherboard Jumper:
In most motherboards CMOS battery is soldered, which makes it difficult to remove the battery. In this case we use another method.
Almost all motherboards contain a jumper that can clear all CMOS settings along with the BIOS password. The location of this jumper varies depending upon the motherboard brand. You should read your motherboard manual to check its location. If you don't have the manual then look for the jumpers near the CMOS battery. Most of the manufacturer label the jumper as CLR, CLEAR, CLEAR CMOS, etc.
When you find the jumper, look carefully. There will be 3 pins and the jumper will be joining the center pin to either left or right pin. What you need to do, is remove the jumper and join the center pin to the opposite pin. e.g. if the jumper joins center pin to left pin, then remove it and join center pin to right pin. Now wait for a few seconds and then again remove the jumper and join the center pin to left pin.
Make sure to turn the PC off before opening the cabinet and resetting the jumper.

B. By Using Software:

I have found that BIOS/CMOS Password Recovery Tool is the most effective.:
BIOS/CMOS Password Recovery Tool is a program that works instantly to remove any lost or forgotten BIOS/CMOS password. Simply boot your PC to DOS and execute the program, and get access to forgotten BIOS/CMOS passwords in just seconds
BIOS/CMOS Password Recovery Tool Service: http://www.biospasswordrecovery.com/