Cannot boot from usb stick

Here's the solution:

The root of this issue is that Macbooks, Mac Pro and iMacs all have a GPT partition scheme. Issue is, even if it reads both schemes, Apple's UEFI (Bios) is more "fluent" in GPT than in MBR... That's why it only detect USB Keys / Drives once a while only.

- To format CORRECTLY a USB key / drive to burn an ISO, follow these 7 steps:

1. On a Windows PC, download Rufus https://rufus.akeo.ie/

2. Select the destination USB Drive.

For USB HDD, click on the arrow next to "Format options" and check "List USB Hard Drives"

3. Don't touch anything yet, go straight to "Create a bootable disk using" and look for your ISO.

4. Once the ISO is loaded, in "Partition Scheme", select "GPT Partition Scheme for UEFI"
Be careful: If you first change to GPT and then select an ISO, it will revert to MBR. If so, choose GPT for UEFI again.

5. In "File System", select "Fat32" (or Large Fat32) if possible, or NTFS.

6. Leave all other options as default, and click START to expand the ISO file to your USB drive key

7. Now on your Mac, make sure it's completely shut down before you insert your USB drive / key.

Then hold the "Option" key and tada... Your USB drive / key should show up in a orange icon saying "UEFI Disk".
Select with the arrows and hit the Enter key.

- If you have Partition compatibility issues while installing Windows 10 on your Bootcamp partition, follow these 4 steps:

You might have an error saying "Windows can't install on this disk (partition) because the scheme is not GPT" or another error just saying "Can't install on this disk" (happens even if we're 100% sure our internal HDD / SSD is in GPT Scheme):
1. You'll need to remove the internal disk and plug it in a Windows PC (using a SATAIII to USB3 cable: Amazon.com: StarTech USB 3.0 to 2.5" SATA III Hard Drive Adapter Cable w/ UASP - SATA to USB 3.0 Converter for SSD/HDD: …)

2. Launch a partition tool (from Acronis, O&O, or my favorite EaseUS https://www.easeus.com/partition-manager/epm-pro.html)

3. Then select the Bootcamp partition of your internal drive (make sure it's the correct one)

4. And the click on "Repair GPT Partition".

If after this, you still have an error on Windows 10, from the installer when you select the Bootcamp partition, just erase the Bootcamp partition (with the pink erasor) and simply click "Next". This way we're telling Windows Installer to just recreate the whole partition the way he wants.

OP: If this solved your issue, please mark this post as Solution to close this ticket.

Hope this helps.

Here's the solution (corrected):

Intro: The root of this issue
Macbooks, Mac Pro and iMacs all have a GPT partition scheme. Issue is, even if it reads both schemes, Apple's UEFI (Bios) is more "fluent" in GPT than in MBR... That's why it only detect USB Keys / Drives once a while only.

To format CORRECTLY a USB key / drive to burn an ISO, follow these 7 steps:

1. On a Windows PC, download Rufus https://rufus.akeo.ie/

2. Select the destination USB Drive.

For USB HDD, click on the arrow next to "Format options" and check "List USB Hard Drives"

3. Don't touch anything yet, go straight to "Create a bootable disk using" and look for your ISO.

4. Once the ISO is loaded, in "Partition Scheme", select "GPT Partition Scheme for UEFI"
Be careful: If you first change to GPT and then select an ISO, it will revert to MBR. If so, choose GPT for UEFI again.

5. In "File System", select "Fat32" (or Large Fat32) if possible, or NTFS.

6. Leave all other options as default, and click START to expand the ISO file to your USB drive key

7. Now on your Mac, make sure it's completely shut down before you insert your USB drive / key.

Then hold the "Option" key and tada... Your USB drive / key should show up in a orange icon saying "UEFI Disk".
Select with the arrows and hit the Enter key.

If you have Partition compatibility issues while installing Windows 10 on your Bootcamp partition:

1. You might have an error saying "Windows can't install on this disk (partition) because the scheme is not GPT" or another error just saying "Can't install on this disk" (happens even if we're 100% sure our internal HDD / SSD is in GPT Scheme).

2. If so, elect the Bootcamp partition, just erase the Bootcamp partition (pink eraser icon) and click "Next". This way we're telling Windows Installer to just recreate the whole partition the way he wants.

OP: If this solved your issue, please mark this post as Solution to close this ticket.

Hope this helps.

http://support.apple.com/kb/HT1948?viewlocale=en_US&locale=en_US

Hmm, when you mean "bootable" are you meaning booting a operating system from the USB to run the computer with?

Because that's what "booting" means, not mounting, which is what I think you mean.

I say this is because you mentioned a PC, and a generic PC can't normally boot from a USB with OS X installed without a LOT of extra help of the hacking/breaking software agreement kind which is beyond the capability of most.

If you mean your USB thumb drive is not mounting or showing up on the computer to trade files, then please tell us how you formatted the USB or if you didn't or not and it's volume size.

Also if it does have OS X on it, what version and where did you install it from, because it might be lacking the hardware drivers for the other Mac.

What are you trying to accomplish?

Have you tried another USB slot on the same computer?

Isolating issues in Mac OS X

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