At times, and without any obvious reason, static discharges as well as other electrical problems can cause the PROM on the motherboard to reset the Bios (CMOS) to its default values and even cause the default Bios password to be set. These are some of the default Bios passwords used with different Bios's, give them a try first.
AMI
Award
bios
setup
cmos
concat
AMI_SW (case sensitive)
AMI!SW/
AMI?SW/
j262
NOTE: With respect to the Award BIOS, the "AWARD_SW" (use without quotes) and (is is case sensitive) password should even override a set password! If not, you may also want try j262 as the password.
Also you can try clearing the bios if jumpers are available
