Hi:
Please refer to page 306 of the service manual at the link below.
You'll just have to look around until you find a green jumper on the motherboard.
They are in different locations based on the model. Normally they are in the vicinity of the coin cell battery toward the edge of the motherboard.
http://h20628.www2.hp.com/km-ext/kmcsdirect/emr_na-c03612798-1.pdf
If following the procedure of removing the jumper does not clear the BIOS password, then stringent security was set and unless you can find someone that knows the password, you will never be able to clear it.