I am using a IMac 2011 core I5 with 4GB ram. I recently had ram upgraded to 16GB and also had my DVD drive replaced with a seagate 250GB SSD in a cradle. After installing High Sierra on it, I reformatted the Main 1 Tera HD. All went well till I hit the restart button. Everytime I restart I get the prohibition sign. I power off the PC wait a minute and power up and it boots up ok. The prohibition sign only appears whenever I do a restart. Would really appreciate any help.

  • Looks like it is trying to boot on the wrong HDD, which could indicate that something remained on it (like: the two HDD has now an active boot sector, but just one is valid and contains boot files..) I would try removing one HD and see if it happens or not. depending on the result, it will be necessary to investigate deeper so we can remove the cause that is confusing it to soft-restart. – Prado Aug 10 at 19:55
  • Thanks, will try to do that and repost result. – jaime MV Aug 10 at 23:27
  • Make sure the correct partition is selected in System Prefs > Startup Disk… not just visible, actually selected. – Tetsujin Aug 11 at 11:31
  • It does boot normally upon power up. Issue is with restart only, its when I get a prohibition error. Pressing power off then back on boots directly to secondary SSD with no issues. I have not tried to remove the HD cable of the original hard drive yet but its really confusing since I already did a 7 pass on it. I have to bring it back to apple service center to have cable removed, they could not get the issue with prohibition resolved reason I pulled it out. Other than that it works fine. Just really restart when I get prohibition sign. – jaime MV Aug 13 at 6:52

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