External Hard Drive Data Loss After canceling copy Operation

Hi All-

I was attempting to copy a 1.7GB garageband file from my macbook air to a shared external drive connected to my office desktop (via wireless LAN) but canceled the operating after realizing that I was copying the wrong file. The copy progress bar froze with the text "canceling" underneath it. I didn't think anything of it and minimized it while I selected the correct file and copied it.

As it was copying the new file over the finder screen started to flash erratically and then all of the files on my external drive save my iMovie library disappeared from the finder. I assumed this was a display issue with the finder so I restarted the machine. However it appears the files were deleted as the hardrive only shows about 250MB of data on the drive (the size of the iMovie file).

Can anyone help me here? Are my files really lost? Any suggestions for recovery? This is really troubling.

Thanks!