The BIOS is the basic instruction set that "teaches" the computer how to access its media. If the BIOS is password protected, the computer will not function without the password. BIOS passwords are used in two ways: To prevent modification of the BIOS settings and to completely stop the computer from booting.

If you forgot the BIOS password, try some of the backdoor passwords that might be in place for some BIOS versions. Following is a list of potential passwords that may or may not work. There's no harm in trying 'em out.

For Award BIOS
AWARD_SW
AWARD_PW
j262
HLT
SER
SKY_FOX
BIOSTAR
ALFAROME
Lkwpeter
j256
AWARD?SW
LKWPETER
syxz
ALLy
589589
589721
awkward
CONCAT
d8on
CONDO
j64
szyx

For AMI BIOS
AMI
BIOS
PASSWORD
HEWITT RAND
AMI?SW
AMI_SW
LKWPETER
A.M.I.
CONDO
589589

For Phoenix BIOS
Phoenix

IBM Aptiva
According to DigiSign Data Security, if you have an IBM Aptiva, you can clear the BIOS information by holding down both mouse buttons until the computer boots. They also mention that Toshiba laptops will bypass the BIOS password if the left shift key is held down during boot.