I was having issues with my battery - it would only charge to 76%, and the HP calibration tool wouldn't work. I ordered a new battery, and upon receipt I opened my Elitebook. I removed the battery following the instructions in the HP video on YouTube. I then discovered I had been sent the incorrect replacement, so I put the original battery back in and reassembled the laptop.
Pressing the power button has resulted in a boot loop of sorts.
Step 1 - the keyboard backlight, along with all of the non-power lights, flash on and off.
Step 2 - The power light flashes white, yellow, white, yellow.
Step 3 - 2 second pause.
Back to step 1 and repeat ad infinitum.
I'm assuming something is broken but don't know what, and the troubleshooting guide doesn't really cover this particular error.