If you have Windows 8.1 or Windows 7 with Service Pack 1 (SP1), the following full-screen notification might appear on your computer:

Sorry to interrupt, but this is important.

Windows 10 free upgrade offer ends July 29.

This notification is a reminder that the Window 10 free upgrade offer ends on July 29, 2016. Microsoft recommends that you upgrade to Windows 10 before the offer expires. You can choose to upgrade directly from the notification, dismiss the notification permanently, or choose to be reminded later. For more information about the Windows 10 upgrade and how to manage notifications, see the "More Information" section.

This message appears when you unlock Windows through the end of the upgrade offer, and reoccurs three days later if you select the Remind me later option.

This message does not appear if any of the following conditions are true:

  • You have a recent version of the "Get Windows 10" app installed.
  • You have selected the Do not notify me again option.
  • Your computer is detected to be incompatible with Windows 10.
  • You have previously uninstalled Windows 10 after you upgrade.
  • Your Windows 10 installation failed and rolled back.
  • You have hidden the "Get Windows 10" app notifications.
  • You have disabled the Windows 10 upgrade or you have disabled the offer screen through registry key settings.

Source: https://support.microsoft.com/en-us/kb/3173040