If you contact HP Enterprise Support (not consumer support), and prove ownership (or pay a $50 fee), they can generate a using that PSID. This code is injected via a USB keyboard on the lock screen.
If the hardware reset failed, the password is stored in a chip on the motherboard. How To Reset Bios Password Hp Elitebook 840 G3
Try Method 1 first. If no "System Disabled" code appears, proceed to Method 2 . If you aren't comfortable with hardware, take it to a local PC repair shop (should cost $30–50). If you contact HP Enterprise Support (not consumer
Some older HP EliteBooks (pre-G4) are vulnerable to a hardware short. This is not recommended for the faint of heart, but it has worked on some 840 G3 units with older BIOS versions (pre-2018). How To Reset Bios Password Hp Elitebook 840 G3