The Book

1. Download HPBR.zip file
2. Insert clean USB flash drive.
3. Run the USB Image tool.
4. Choose the flash drive then click on RESTORE.
5. After restore remove flash drive.
6. Insert flash drive into locked laptop and boot. (If HDD is installed remove before booting.)
7. At C:\OUTPUT type CD.. “Then hit enter”
8. Type HPBR “Then hit enter”
9. Select #3 re-program. (to save your settings)
10. Press “S” to save system information.
11. Type HPBR and hit enter.
12. If your model is not listed select “SHOTGUN.”
13. Reboot
14. After reboot repeat the procedure (without 8. 9. and 10.) and select “SHOTGUN” a second time.

The BIOS should be unlocked now.

HP Support Forum thread - http://h30434.www3.hp.com/t5/Notebook-Hardware-and-Upgrade-Questions/ProBook-6540b-BIOS-locked/m-p/5521515#M329535