Boot Camp: Press any key message appears while installing Windows 8 using DVD media (Apple KB)

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When installing Windows 8 on an iMac (Late 2013) or Mac Pro (Late 2013), installation may not complete if you use an optical disc for installation. Instead, you are prompted to "press any key" or the computer restarts back to OS X.

Read more: http://support.apple.com/kb/TS5373