the fast and sure way of resolving that bios password issue is by sending the machine to an authorized Compaq/HP service center. Although this would cost you some amount for service charge, this is the safest way. The authorized Compaq/HP service center would know the exact password reset procedure for the bios.
usually the bios reset procedure is not disclosed on manufacturer websites and manuals -- as they consider this to be a system protection feature that is the user's responsibility. The BIOS password is an optional security measure against theft or unauthorized computer access to protect the user and his computer.
this page is the Compaq support page and instructions for finding an authorized service center Using a Certified HP Service Center to Repair a Notebook PC Compaq Presario V4000 Notebook PC - HP Customer Care (United States - English)
================================= Free and DIY alternatives
that could void your computer's warranty
(but this would be good if the system is no longer in warranty AND you prefer to explore/risk with a DIY procedure first, AND, you think that sending to a paid service center would be a last resort) 1. Ultimate Boot CD --> CMOS Password reset tools
The "Ultimate Boot CD" is a compendium of diagnostic tools. One component of the ultimate boot cd are BIOS/CMOS password reset tools. Depending on the BIOS brand and model, the tools in the Ultimate Boot CD can attempt to reveal the bios password OR try to reset it back to nothing.
You may downlaod the Ultimate Boot CD from its website Ultimate Boot CD - Overview
, burn the ISO file to a bootable cd, and then use it to boot the laptop (if this is possible)
Or, you can choose to burn the ultimate boot cd into a flash drive, and boot from the usb flash drive instead. The procedure for doing this is here: http://www.syschat.com/how-run-ultim...lash-6869.html
================================= 2. Open the laptop, locate and disconnect the CMOS battery
Since BIOS time, date, motherboard settings, and even BIOS passwords are saved through the charge kept by the CMOS battery, locating and disconnecting the cmos battery will remove the bios password.
from previous posts here about bios problems, below are pictures that you may find helpful for identifying a laptop cmos battery
On some laptops, the cmos battery may be covered in a plastic container that is connected with two wires. It really depends on the motherboard manufacturer. if you spot something that looks like a circular battery, see if it can be removed by simply unticking it out of the latch, or unhooking the wire connectors that may attached to it.
below is a screenshot that i took of one of the HP laptop video tutorials. The actual goal of the tutorial is to instruct on the replacement of the wireless lan card. luckily, we've spotted something that looks like a cmos battery container underneath the wireless lan card. http://i51.tinypic.com/2whmo1e.jpg
for your laptop Compaq Presario V4000, the tutorial links below show steps on how to detach internal parts like ram, hard drive, cdrom, wireless lan card.
i suggest you take time to watch these videos, and when are confident with removing hardware, do try to reattach the parts. you might find something similar to the cmos battery, and maybe detaching for some minutes and then booting the computer would indeed clear the saved bios password.
Tutorials: Adding / Replacing hardware Compaq Presario V4000 Notebook PC - HP Customer Care (United States - English) Steps for Removing and Replacing the Hard Disk Drive Compaq Presario V4000 Notebook PC - HP Customer Care (United States - English) Steps for Removing and Replacing the Wireless LAN Mini PCI Card Compaq Presario V4000 Notebook PC - HP Customer Care (United States - English) Steps for Removing and Replacing the CD or DVD Drive Compaq Presario V4000 Notebook PC - HP Customer Care (United States - English)
again, the safest way is to have an authorized Compaq/HP service center attend to this bios password problem.
doing the manual DIY detaching of parts and hardware might void your existing warranty.
goodluck on this