I have a (August,2007) Macpro1,1 which I have been trying for a week to install Mountain Lion on…following the Jabbawok install procedure. After many misfires, I finally installed ML on a dedicated (GUID formatted) hard drive…at least all indications were it installed.
However, even though it showed up in Preferences Start-Up window, and also when I started up holding the Option key, I immediately get the gray screen with the slashed circle.
I need someone with more knowledge than me to advise as to whether my particular macpro needs different settings than the 2006 model instructions.
Can you email me your contact info … I would love to chat.
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