Need to boot from bootable USB - but no option to do so

Need to boot from bootable USB - but no option to do so

I've downloaded Linux (Elementary OS) so I can start writing code in Vala
in my spare time, but there is a problem.
I bought a new PC last month, it's an All-In-One (HP Pavilion something
something etc) and when you turn the computer on, you normally see the
command-prompt-style-interface for a little while with the 8-bit looking
text with options down the bottom of the screen, like um, F7 and F10 to
enter setup mode, etc.
But not on this computer. The only thing you see from the time you press
the power button, till the time Windows asks you to sign into your
account, it the HP Logo and the Windows 8 progress ring (the circle dots
that appear when something loads). Nothing else.
I have tried pressing F7, F8, F9, F10, F11, F12 etc during the startup
process but have not been able to get into BIOS settings so I can set the
USB as the boot device.
I also went into Control Panel > System > Administrative Tools > System
Configuration, then Boot tab, and there is only one drive listed - which
is the PC's internal hard disk.
And there appears to be no option to select something like "Boot from
other device or USB" or anything like that.
What are the different ways one can change Boot priority/what to boot with
in Windows and how can I get it to display BIOS settings when the options
aren't even displayed?
And if you have any experience with this computer, please do let me know
how to boot into BIOS while starting up the PC.
Any help is much appreciated. Thanks!