External Drive not working

Some how my previous post got dropped.  I purchased a 500GB external passport and everything seemed ok at first, but the second time I tried to use it I was told that the drive needed to be formatted.  I was a little ticked off, but I formatted the drive again and downloaded my stuff again.  A couple of days later the same thing again.  What is the deal?  Has anyone else experienced this?  Any words of wisdom, or did I just purchase a defective drive?

Are you removing the drive proplerly or just pulling the plug?  If not that can corrupt the drive. Also are you using this on more than one PC and XP and Vistaor Windows 7?