Says PID 0 prohibited (that's the kernal). NVRAM or PRAM (in older Mac computers) stores the information about system settings such as the startup disk to boot your Mac from, system date and time, screen resolution, etc. But it won't boot. Macbook keeps rebooting on installation USB after trying to reinstall - EFI partition empty. As a result, booting from USB media is becoming the standard. Either way, here are the troubleshooting steps you should take to fix a Mac that won’t boot. I've been messing around with partitions and setting up triple boot (linx,windows,mac). If any of these information gets corrupt, your MacBook Pro may fail to start properly or won’t start at all. My Mac won’t turn on — now what? And while users historically would pop a boot media disk into their DVD or CD drive, many computers no longer come with optical disk drives. 1. If you have bought an M1-based Mac or MacBook but need to upgrade your storage without buying a brand new device, you can set up your Mac to run from an external drive. Specifically, the Lion thumb drive that I made a few months ago worked fine with an early 2008 MacBook Pro, but didn't show up in the boot picker on a mid-2007 MacBook (MacBook2,1) or a 2008 Mac … 2. I guess I'm out of luck. Here's how to boot … The older MacBooks & MacBook Pro’s didn’t offer USB boot support. Again, after having waited 30 minutes the USB won't show up. Mac won't boot from USB drive: Prohibited sign. I plug it into the Thunderbolt-2 port on the Mac Mini, and the computer *does* see that partition, but it won't boot to it -- the computer simply turns itself off after about 5 seconds of trying to boot to that drive. For desktop Macs, a cable may have come unplugged. 1. Now when I boot, that SSD freezes up my BIOS. 1. It does not prevent booting from external drives. MacBook Pro, 15" (Early 2011), not booting. Question: Q: Macbook Air Won't Boot from USB Stick. 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). I waited exactly 30 minutes and it still won't show up. Or would you have more ideas I could try? This may sound obvious, but check to see if your Mac has power or if its battery needs charging. The first Mac was the MacBook Air which came out in January 2008. I run diskutil force unmount for each disk successfully but it still won't unmount the main disk. I take SSD out, try putting it in a USB hardrive tray reader, nothing. I'm having an issue all of the sudden with trying to restore Lion on my Air. Indeed, I ment that I only get the option to booth from HDD, the USB drive is not shown as an option to boot from. 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