You can just use Disk Management to format any drive which is properly connected and which appears in Disk Management.
The partition/drive does not necessarily have to be reflected in My Computer, since My Computer only reflects partitions/drives which are formatted with a file system...signaling that the partition/drive is ready for use by Windows.
I guess that I'm somewhat concerned by "Just couldn't view them from my external".
That could indicate a problem with that drive itself, in which case I would run a manufacturer's diagnostic on it before taking a chance on future use.
Hard Drive Installation and Diagnostic Tools - http://www.bleepingcomputer.com/forums/t/28744/hard-drive-installation-and-diagnostic-tools/
Some disk problems can be overcome by formatting, some cannot.