Hot answers tagged boot
You do have a recent backup? If not this procedure will be substantially different. Backed Up? Use Recovery Mode If you boot into recovery mode using Command+R at startup can you proceed with an internet recovery by installing over top of the hosed OS already on the drive? If that works I would try that first. It should leave your files and apps alone ...
You may want to look at the help provided here on identifying and downloading a new copy of AHT for your specific hardware. Once you have AHT back in the .diagnostics folder (you may find you don't even have a .diagnostics folder now) you should be able to run AHT using the 'd' key on startup.
@Tetsujin is completely correct about the disk. My first hope is that you have a recent backup. If you don't, try to get one, but if the disk is actually the source of the problem, getting a new backup may be difficult or lengthy. If you don't have a recent backup, you Time Machine with an external hard drive will produce one for you. My preferred ...
NVRAM holds the info on where/how to boot (Target Disk Mode). You need to reset the NVRAM
That looks like the Thunderbolt logo. Your Mac probably thinks that is in Target Disk Mode.
Let me know if anything goes wrong! I have tried to update everything for the latest version of VirtualBox, but I may have messed up somewhere... The method I use relies on VirtualBox for its operation. Follow these steps: Install the latest version of VirtualBox from https://www.virtualbox.org/wiki/Downloads. Make sure it installs the command line tools. ...
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