tumppiw wrote:

Another possibilty is the keyboard is connected to a USB3-port, at which
point it wont be recognized until Windows has loaded USB3-drivers..

Some mobos' firmware support "legacy USB3" devices but it must be
enabled in the UEFI (and not likely an option if using BIOS). The lack
of firmware support for USB3 is why pre-builts still come with both USB2
ports and add USB3 ports.

I looked at the HP documentation (if what I found at HP matches what the
OP says he has). No mention of USB3 in its manual. Its specs are at:

http://support.hp.com/us-en/product/...ent/c03066698/

Looks like that model came out in 2011. So it is not a pre-built that
came with Windows 10 pre-installed nor did it come with USB3 ports. His
mention of "even with Windows 10" implicates that he installed Windows
10 meaning something older came on that PC. When I look at the drivers
section of the product page, only Windows 7 and 8 are listed as
supported. So the OP is trying to use a later version of Windows than
for what the hardware was designed to support. Because there are no
drivers from HP for that mobo, there are also no chipset drivers to
enable support to provide an interface between the OS and hardware.
Windows 10 probably has to use old drivers for that old hardware.
Chipset drivers aren't loaded when the BIOS loads. Those load when the
OS loads and then loads those drivers.

I would think the old drivers included in Windows 10 would support the
USB3 ports on the old mobo - but, as you say, the old BIOS firmware
might not. That model did not come with USB3 ports but maybe he or his
buddy added a USB3 card. If so, he should connect his USB keyboard and
mouse to a USB 2 port.