Chances are you installed a windows update to your server that caused this to occur. There was some in April and May 2016 time frame that were released.
Completing the post installation tasks will resolve the issue:
Microsoft Warns WSUS Users About Flawed KB3148812 Update
If you get this message when try to edit a maintenance task:
‘Agent XPs’ component is turned off as part of the security configuration for this server. A system administrator can enable the use of ‘Agent XPs’ by using sp_configure. For more information about enabling ‘Agent XPs’, see “Surface Area Configuration” in SQL Server Books Online. (ObjectExplorer)
Chances are your MS SQL Agent isn’t running. Just start the service and you should be good. I would recommend going into servers and setup a recovery option to restart upon failure, this will keep a watch over it and start it if its stopped.