We have had good luck with a couple devices by updating the BOIS... According to that link are you having the slowness of the preboot screen showing up?
We had to disable the fast boot but the latest BIOS fixed it for the HP Revolve G2.
Also forgot to mention trying going into the BIOS before the preboot screen comes up and then just exit to see if the keyboard / mouse works.
If it does then you may have to call HP support and start the process to get it fixed.
Youngs' suggestions are very good. To elaborate on them:
1. Setting fast boot to thorough ensures that all the protocols are available rather than the minimum required to load Windows
2. Booting to BIOS (UEFI setup screen) and then exiting or booting to the UEFI Boot device selection screen and selecting to HDD will initialize the KB / Mouse protocols and thusly available to the PBA application. If this works, the UEFI is likely blocking the protocol initialization request from the PBA application and will need to be addressed by HP in a UEFI firmware update.
I would also suggest testing with a fresh activaiton (not an upgrade) of MDE 7.1.3 and the newest version of the Hardware Default Product Detections XML attached to the bottom of KB81900.
My company actually initiated this KB article with McAfee and I worked with HP engineers. You need to contact HP Support and get the BIOS update 1.05. It is a beta bios and has not been released yet, but we are running it on our M71 laptops with no issues.