Well if you have a pendrive that you haven't used on Linux that can't be detected by Windows then I would think you have a problem with Windows, not the pendrives. Anyway you can't damage a drive just by reading it from Linux, only if you unplug it without unmounting it first (Linux equivalent of 'Safely Remove Hardware'). If you have unplugged the Seagate without unmounting it first then it is possible you could have damaged it, but on the other hand if you saw no icon for it then maybe it wasn't mounted in the first place, in that case you are perfectly safe. Did you access the Seagate at all? (ie read from it or write to it?).
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