How to fix Seagate 500gb external Hard Drive corrupted after Linux backup?

HI
Once I tried to take a backup of a PC with fedora 17 to my friend's external hard drive. It was a 500GB Seagate HDD. Since I am a newbie to Linux I have used a command that I found online. However the backup process got interrupted halfway. After that I can't use it in windows and the drive doesn't even showing in my computer. Please somebody tell me how to fix it?
