Some people have complained that they can't install Linux on new machines because their firmware won't let them choose a boot device. This is part of Windows 8's fast boot support - the keyboard may not be initialised until after the OS has started. To deal with this, insert the install media and reboot your computer. Wait for Windows 8 to start. While holding down shift, click on the power icon and click on restart. When the menu appears, click "Use a device" and then click your install media. If it's listed more than once, choose the one that says "UEFI" in front of it. Your system will now restart and boot off the install media.