imac won't boot when usb plugged in

Question

imac won't boot when usb plugged in

Hi all,

I have a probleme since i got my Imac 27 Mid 2010. It just dont boot when a usb Drive is plugged in. I had i Firewire hard drive in the past and i had no problems to boot up on it. Turn the mac on, holding option key and bang ! BUT usb just dont work, it stay on gray screen and after a while (10 mins) it boot on my regular internal drive.

I tried several usb drives and it's always the same. It look's that im not the only one that have this problem. I bought this fantastic Machine but i cant make a rescue clone and that driving me crazy !! I think my situation is not ''NORMAL''

Thank's all

iMac (27-inch Mid 2010), Mac OS X (10.6.8)

Posted on Jun 17, 2012 7:15 AM

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Answer 1

rkaufmann87

Level 10

140,796 points

Jun 17, 2012 7:17 AM in response to jocelynfromst-hubert

Please click on the iMac SMC and PRAM reset link and perform each reset. Sometimes you may need to do each 2-3 times.

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Answer 2

Jun 17, 2012 9:33 AM in response to jocelynfromst-hubert

Hi,

Thanks, but it does nothing. I done the procedure 3 times. I dont know what to do!

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Answer 3

RRFS

Level 5

4,522 points

Jun 17, 2012 9:57 AM in response to jocelynfromst-hubert

Are you using thumb drives? Did you format them GUID for the OS installation?

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Answer 4

den.thed

Level 9

77,332 points

Jun 17, 2012 10:02 AM in response to jocelynfromst-hubert

Intel iMac's can boot from either a FireWire or USB drive, but only if the drive is properly Partitioned and Formatted.

What are you using to make your Rescue Clone, Disk Utility, CarbonCopyCloner, SuperDuper or something else?

Some Utilities will setup and bless the drive for Bootable Cloning, but most of the time it is best to manually set the Partition Map Scheme to GUID Partition Table and the Format to Mac OS Extended (Journald) using Disk Utility.

see > OSX Tips: Using Disk Utility 1. Format, Erase, or Reformat a Drive

or > Formatting & Partitioning a Hard Drive in OS X

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Answer 5

Jun 17, 2012 10:22 AM in response to jocelynfromst-hubert

I am using CCC to clone my drive. When my USB drive (laCie external drive W a WD 500GB Black) is unpluged, and i press option key, it ask me if i want to boot on osx drive or windows Bootcamp.

But when my external drive is plugged, Gray screen untill i unplug the external drive ???

The drive is well formated with a guid partition and extended (journalid)

AS i said, the mac boot ok on external drive firewire

Thanks

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Answer 6

RRFS

Level 5

4,522 points

Jun 17, 2012 10:27 AM in response to jocelynfromst-hubert

SMC RESET

http://support.apple.com/kb/HT3964

Shut down the computer.
Unplug the computer's power cord and ALL peripherals.
Wait 15 seconds.
Attach the computers power cable.
Wait another 5 seconds and press the power button to turn on the computer.

(this reset depends on the 5 second timing for it to work)

PRAM RESET

Zap the PRAM

Shut down the computer.
Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
Turn on the computer.
Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
Hold the keys down until the computer restarts and you hear the startup sound for the second time.
Release the keys.

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Answer 7

den.thed

Level 9

77,332 points

Jun 17, 2012 10:36 AM in response to jocelynfromst-hubert

That's starting to sound more like a bad cable or the drive enclousure.

I might try another USB port and another cable, then if it still refuses to work another USB drive.

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Answer 8

rkaufmann87

Level 10

140,796 points

Jun 17, 2012 10:43 AM in response to jocelynfromst-hubert

It's actually 2 resets, you did each 3 times? If so then try restarting in Safe Mode. To do that, when you hear the startup tone hold down th Shift key until you see a progress bar. A Safe Mode restart clears some caches, it's possible one or more is corrupt.

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Answer 9

Jun 17, 2012 4:47 PM in response to jocelynfromst-hubert

Hello,

The drive work very well, one of the best i ever had. I tried dieffrent disk in the enclosure and another cable !

I booted in safe mode and some changes happend to my secondary screen and bluetooth BUT nothing for the usb boot. Same as usual 😟

Thanks

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Answer 10

X423424X

Level 6

14,265 points

Jun 17, 2012 5:02 PM in response to jocelynfromst-hubert

It may work "very well" but different makes of enclosures have different bridge firmware for the electronics that bridge between the USB and SATA. From what I read in this thread I suspect that bridge firmware is not mac compatible to the extent that it won't allow you to boot.

Exactly what brand and model is that enclosure?

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