Are these drives out of Mac laptop? If they are formatted for Mac that would explain it...or Linux
A proper Disk Partition utility should let you see the whole drive...
Are you sure you are connecting the HDD's up properly in the USB enclosure?
A working USB interface improperly connected to a hard drive could appear as an unformatted drive.
I'd make absolutely certain that the drive was properly connected to the interface card that's in that external enclosure. Double (even triple) check that all of the assembly instructions were followed and that the drive is attached the right way.
Try plugging the USB cable into a different USB port on your computer, or try it in a totally different system if possible...might be some weird USB incompatibility...
If still no luck then try this:http://blog.paulgu.com/windows/delete-g ... partition/