That is exactly what happened to me last week. The Disk Management tool has just overwritten the APM with a Master Boot Record (MBR) and all partition information seems lost. Cause “initialize” means something entirely else. You hesitate for a second, but decide it must mean something like “just start the damn thing up, so that it works” (later on you know that this must have been your weakest moment of that day, maybe even the entire week, but at this “moment suprême” you feel it’s the only choice). When you right-click the symbol, you’re able to “initialize” the drive. You check the Disk Management tool and you notice a red stop sign on the external drive. You’ve installed MacDrive on it, but somehow it doesn’t recognize the volumes that are on it. You’re happily using it on your Mac and for some reason you’ve decided to hook it up to a Windows PC. It’s Apple Partition Map (APM) partitioned and contains a couple of HFS+ Journaled formatted volumes. Say you’ve got an external harddisk in a Firewire or USB enclosure. I haven’t used it, but it looks very promising!.

It’s called TestDisk, open source data recovery software. I just came accross an open source piece of software that might do all of the manual work described below for you.

Testdisk osx