“…registration is officially open for the Windows Upgrade Offer…If you purchase or have purchased an eligible Windows 7 PC anytime between June 2, 2012 and January 31, 2013 you will be able to purchase an upgrade to Windows 8 Pro for only $14.99 (U.S.)…
“Registration for the Windows Upgrade Offer is only for those who buy an eligible Windows 7 PC between June 2nd and January 31st, 2013.
“Did you already buy an awesome Windows 7 PC prior to June 2nd (or have a Windows 7 PC not eligible for the offer)?…Starting on October 26th, you will be able to upgrade to Windows 8 Pro for $39.99!”
https://windowsupgradeoffer.com/