The Intel Management Engine firmware must be (i.e., a stock ME region replacing the original) if the system fails to POST after reprogramming. Using a raw backup of a different unit may cause boot failure due to cryptographic pairing.
The HP EliteBook 840 G5 is a robust business machine, but like all laptops, the BIOS firmware can become corrupted. This often happens due to a failed update, a virus, or a dead CMOS battery. Typical symptoms include:
Before attempting any repair, identify your hardware.