SharePoint 2013 Sandbox solution cannot be activated (activation button is not available)

Upload the sandboxed solution to the solution Library of the target site and discover that the Activate button is grayed out and unavailable.

first of all , I think of insufficient permissions, so "as administrator" to start IE, and then found still unable to activate.

is the sandbox service not started? To view: Central Administration------System settings-------Services on the Management Server

Sure enough, "Microsoft SharePoint Foundation Sandboxed Code Service" did not start.

Start it, and then you can activate your sandboxed solution (try uploading the WSP file again if it doesn't work).

Of course you can also start it with the PowerShell command: Start-service-name SPUserCodeV4

SharePoint 2013 Sandbox solution cannot be activated (activation button is not available)