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IMac is not detecting external USB hard drive

Update:11-30Source: network consolidation
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I restored my iMac (mid 2011 - i5 quadcore - 1TB - 16gb Ram - Lion 10.7.3) and my Macbook Pro (2010 Core 2 - 8gb Ram - Lion 10.7.3) I have a 1TB Toshiba external portable USB 3.0 hard drive.
The drive connects and recognizes quickly and works without any issues on the MBP, on the iMac on the other hand it will not detect in system profile or disk utility. Occasionally when plugged in the drive will spin up and stay powered on, other times on plug in, the indicator light will flash quickly and power off. The drive is fairly new, lightly used, and I repeat has NO issues with the MBP. The iMac will read flash drives and USB devices without issue except for this external hard drive. Also when I restart if the external drive is plugged it it will hang until I remove it. Drive is partitioned 86gb in MS Dos with Master Boot Record profile, and the remaining space is partition 2 formated as Mac journaled.
I am up to date on all updates from apple, and at a complete loss as to what to do next.
Thanks in advance for all your help

The Best Answer

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What version of firmware are you running on the 802.11ac?
There is a 7.7.1 update with USB fixes - http://support.apple.com/kb/DL1665
After my update to 7.7.1, I still cannot see the Seagate 3TB HDD.
The disk works on a 2nd Gen 802.11n Extreme.
This is
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