Undo the CLEAN command on the portable hdd : DISKPART

testdisk might be able to fix that.

1. Download System Rescue CD (live cd) and burn it to a disk or just download testdisk
2. run testdisk
3. choose to create a log file
4. choose the disk that you ran clean on
5. choose intel
6. choose analyze
7. choose quick search
8. confirm to preceed
9. testdisk should find the deleted partition
10. confirm to save the partition table.
11. check for files.

If there's data on the disk that needs to be recovered, don't do this!

You'll need to recreate a partition and format it. Diskpart is capable of doing both:

• select disk 1 or whatever number refers to your hard drive, use list disk to find out.
• create partition primary will create one large partition. Use help create partition primary for more options.
• select partition 1
• format quick to create the file system. Once again, check help format for more options.