|Check Device Manager for Yellow "!" or "?" on the Usb Systems.|
Try plugging the HDD into a different USB Port. It's self powered so you needn't worry about finding a Powered USB Port. If the Same thing happens it's most likely something in the External drive, not necessarily the HDD.
Contact Seagate Support, the Unit should still be under Warranty.
There is nothing to learn from someone who already agrees with you.