The first mac was the macbook air which came out in january 2008. Using an external source like the usb drive helps the user get around the problem.
Click the locked icon and then enter your administrator password.
Mac won t boot from usb drive prohibited sign. Go to apple menu system preference then click startup disk. Booting the mac from usb in a way gives the power back to the user. Insert the bootable usb into mac and power it on.
As soon as the startup process begins hold down the option alt key and keep it depressed until you see the. Select external drive as the startup disk then restart your mac. The older macbooks macbook pro s didn t offer usb boot support.
You will now see the various startup disk options and your usb will be listed. It s been a while that i ve had to worry about it but i do believe the 2007 2008 models are the last ones that required boot up from either the internal optical drive or an external firewire drive prepped with mac os x as a bootable drive. If your mac is using a firmware password the lock icon appears when you try to start up from another disk or volume such as an external drive or macos recovery enter the firmware password to continue.
Provided the system s hardware is working properly then you may see a blinking question mark if a boot volume cannot be found but beyond this you may see a prohibitory sign show up on the screen. Reasons for mac boot from usb. There are a couple of bootup warning signs that may occur with the mac os the most common of which is the folder with the blinking question mark which means a valid start up disk has not yet been.
The likeliest of the reason for choosing the boot from the usb method is that your mac won t start which denies the user access to the computer. Here are the steps to be followed.