I set the External Hard drive to backup which it appears to do successfully until it gets to the imaging of the computer then it quickly finishes and then says Backup was not successful. I've tried it so many times.
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What external HDD are you using? Does it have it's own backup application or are you running a program on the PC? Are you aware that W7 (and probably W8) have a very good native backup facility? I use it weekly to backup my entire C drive to an external HDD. It works well.