Mac doesn't recognize hard disk - that's the reason

Everybody knows this: A new hard disk or another storage medium is connected and the Mac doesn't recognize it. OS X can't find the drive, and it doesn't show up anywhere. The trigger for this can have a number of causes.

Why doesn't the Mac recognize the hard drive?

Once you have connected the hard drive to the Mac, you should check the power supply. If the small power LED is lit and blinking, then it is not a power problem. However, there are some other errors that can cause the behavior.

1. First, disconnect all other peripheral (external) devices from the Mac and connect it to the power supply and power.
2. If it is an active hard drive, i.e. one with its own power supply, connect it to the power supply as well.
3. Now connect the hard drive to the Mac.
4. If this is still not recognized, try a different connection.
5. If this does not help, try to restart the Mac and see if the hard drive can now be found in the Finder.
6. If this is not the case, open the "Disk Utility" and search for the hard drive with "Command + Space".
7. It may be that the hard drive is incorrectly formatted. Löschen Sie die Festplatte im Dienstprogramm mit dem „Entfernen“-Knopf und formatieren Sie diese neu.
8. Achtung, hierbei werden alle Daten, die auf der Festplatte sind, gelöscht.