BIOS unreadable at boot

[Will Mengarini <seldon@eskimo.com>]

I am trying to install Debian on a new prebuilt, but when I
boot and press <F2>, the screen is garbled.  Windows later
figures it out, but by that time it's too late to tell the
BIOS to boot from a USB stick on which I've installed netinst.

The mobo is a Gigabyte B450M DS3H WIFI (rev 1.5), manual at
<https://www.gigabyte.com/Motherboard/B450M-DS3H-WIFI-rev-15#kf>.

I can see some letters on the garbled screen, but have not
yet been able to figure out how to get to the boot order.

So, either of 2 things might help me:

(1) The complete key sequence at the BIOS screen (or its <F1>
help screen) to tell the mobo to boot from the USB stick first.

(2) Some way to boot that stick or its
contents directly from inside Windows.