'deep reset' ???? - I think the G4's still have that available - though youy've probably already tried it!!! - start her up holding down the power button but wait til after the 3rd 'bing' then release .....~ its been a while so I don't remember if thats exectly how it goes ........ but the 'deep reset' certainlgy used to solve some G4 issues
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=== Update (02/04/2017) ===
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..and of course that particular formatting may only apply to internal, not external, hard drives
'deep reset' ???? - I think the G4's still have that available - though youy've probably already tried it!!! - start her up holding down the power button but wait til after the 3rd 'bing' then release .....~ its been a while so I don't remember if thats exectly how it goes ........ but the 'deep reset' certainlgy used to solve some G4 issues