In Windows 8 they dropped the use of the F8 key to access the boot menu.
Now to access such menu you can hold Shift before you press Restart (so already within Windows) and you'll be presented with it after the reboot. Another way is to press "Restart now" at the general PC settings:
As usual, Windows automatically shows the menu when it detects an error and can't continue booting anyway.
You can find more information about it in a TechSpot article or this blog post at MSDN.
To proceed with a recovery process once there go to the troubleshoot menu and select to either refresh or reset the machine. You can find some more information about the process in this other question's answer.