Open the Control Panel, then the "Action Center" icon, then "Change Action Center settings" in the upper left, then "Windows Update Settings" in blue, toward the bottom, then place a CHECK in the box next to "Give me updates for Microsoft products.......".
Of course, you it is possible to fix the problem by logging in as a different administrative user, not the one you normally use, (if you don't already have a second user with admin rights, you should have, so create one now in the Control Panel-User Accounts-Manage another account-Create a new account section) and change the Windows Updates setting there after logging in to the new account.. It will be merged into all admin users settings.
Hope this helps.
Grif
Using Windows 7 In windows update i accidentally unchecked the box for microsoft updates and now the box is gone and i can't get it back. When i checked get updates for other microsoft products find out more it just shows me use start menu to check for updates. Under the setting the box is still not available.

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