I've had that on a work laptop (also an HP). You can try to
disable
secure boot in the UEFI screen, or you can try and tell the USB stick
to treat the laptop like a BIOS machine.
The problem is that changing those settings now will break the existing
Windows install.
Hi
On a recent laptop, Asus X751L, I disabled secure boot. It didn't break
windows8 install (to keep warranty) at all.
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Maderios