You connected it to a Mac,
the Mac asked if you wanted to use that drive as a Time Machine Backup device,
You said Yes,
The Mac told you that it was going to format the drive,
you said OK
The Mac formatted the drive as Mac OS X Extended(Journaled) and killed all the data on the drive.
I have a 'My Passport' external hard drive that was used to back up all files on my HP. Worked fine. I plugged it in to an apple mac to back up those files but the apple cleared all the info on it, renamed it something else (time capsule or something) and now I cant access it on my HP (it shows up in the eject media part but not in 'my computer') How do i get it back to workj on my HP?