Issue with LION on an external HDD

Hi all. This is my first post to this forum so please, be gentle.
I recently had my iMac HDD upgraded from 500gig to 2TB and now I'd like to grab some old files off my original HDD. To do this I bought myself a cheap Dynamode SATA USB docking station and ran migration assistant. MOST of the files copied across but some (my movies, a bunch of applications & some work) didn't.
Unfortunately now it seems my machine won't mount the drive again. Is there some clever way I can force it to mount or check why it's not?

Open Disk Utility and plug the drive in. It should at least pop the name of the drive up in the left window pane. From there, you should be able to run Verify/Repair Permissions and Verify/Repair Disk (if need be). You can also select the drive and use the "Mount" button to force it to mount.

cwa107 said:

Open Disk Utility and plug the drive in. It should at least pop the name of the drive up in the left window pane. From there, you should be able to run Verify/Repair Permissions and Verify/Repair Disk (if need be). You can also select the drive and use the "Mount" button to force it to mount.

Click to expand...

I tried that but the disk doesn't appear on the left. It should right?