I take it you went through these steps:
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Recovering the BIOS using key press combination
When you upgrade the BIOS on your PC, a copy of the previous BIOS version is stored in the HP_TOOLS partition of your hard drive. Many HP computers have an emergency BIOS recovery feature that allows you to recover and install the last known good version of the BIOS from the hard drive, as long as the hard drive remains functional. This emergency recovery feature is separate from the BIOS and is designed to work in the event of a catastrophic BIOS failure.
To recover an earlier version of the BIOS on your PC:
Turn off the computer.
With the computer off, press and hold the Windows logo key and the B key at the same time.
Still pressing those keys, press and hold down the Power button on the computer for 2 to 3 seconds, and then release the Power button but continue to hold the Windows and B keys until the BIOS update screen is displayed or until you hear a beeping sound (usually 8 beeps).
The power LED light remains on, and the screen remains blank for about 40 seconds before anything appears on the display. You might also hear beeping sounds. Eventually, an HP BIOS Update screen displays and the BIOS update begins automatically."