I returned to my MacBook after a few days of not using it, and there was a message that the system had run out of application memory (weird...). So, I followed the recommendation and Force Quit a bunch of applications. In order to just "start fresh", I decided to kill all applications and simply restart the whole machine.

Now that I've killed the applications and restarted the computer, it won't boot. It simply displays a gray circle with a white lightning bolt on it, moving around the screen, screensaver-style. If I unplug the AC power cord, a battery indicator is displayed at the bottom of the screen.

I attempted an SMC reset, but that doesn't help. What's going on, and what should I do?

enter image description here

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    That was it! My keyboard is broken (it usually continually types the letter "T", so I have to disable it and use an external keyboard). So, when I rebooted, the system interpreted the keyboard's input as "use Target Disk Mode". I simply held down the "Cmd" key so that it became "Cmd-T", which prevented TDM. I've successfully booted! – rinogo Sep 28 '15 at 14:27
  • If you add an answer in this regard, I'll accept it. Good to have this knowledge stick around in the rare case someone else has the problem! :) – rinogo Sep 28 '15 at 14:28
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    Good to hear that your Mac works! I'll add my comment as an answer, then. – RedEagle2000 Sep 28 '15 at 14:28
  • Me ttttoo. Thanks!ttttttttttttttttttttttttttttttttttttttt – Jamey May 8 '17 at 16:13
  • Seriously, me oo! apple.stackexchange.com/questions/297518/… Did you need a hardware fix in he end? – Synesso Sep 12 '17 at 1:17

That looks like the Thunderbolt logo. Your Mac probably thinks that is in Target Disk Mode.

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    It was TDM! See my comment on the original question for what I did to "fix" the problem. – rinogo Sep 28 '15 at 14:29
  • Wow ... have the same problem with the same letter t busted on the built in keyboard. Is it worth replacing the keyboard? – Manfred Moser Dec 4 '18 at 15:49
  • I have the same problem (non-working/repeating "t"). Apple (Genius Bar) said it would cost $475 to replace the keyboard, because they have to replace the screen at the same time. Still a lot cheaper than a new Macbook Pro, so I'm going to do this. – John Broughton Feb 27 '19 at 19:01

NVRAM holds the info on where/how to boot (Target Disk Mode). You need to reset the NVRAM


Watch on the right of your mac, on top it has the same symbol as the logo you are showing. It is probably a cable that needs to be plugged in. If you think this means trouble go to your local apple store.

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