On Sept 21, I downloaded a new security update (10.11.6) on my Mac mini (late 2010). On Sept 23, I did a backup to my Time Machine, then shut the Mac down for a weekend vacation. On Monday, I booted up and the Time Machine icon was missing from my desktop. Power and firewire cords were tight (I can hear it running). It was turned “on” in Preferences but said it was not connected. Disk Utility did not show the drive at all. I switched out the firewire with a USB cord and the icon appeared…for 2 seconds. Could this problem be connected to the update? Or is it time for a new Time Machine?