External USB Hard Drive not recognized on iMac HELP!!

Question

I am currently using a i5 iMac running Lion 10.7.5
I have recently partitioned a Verbatim USB external hard drive and uploaded all my footage from a wedding. This was done with no problems and the QT videos could be opened from the hard drive.
A few weeks later, the hard drive does not show up in my finder. BUT it is recognized in disk utility. Here is a screen shot;
So first I ran "Verify" and it told me to repair disk. After clicking on Repair, I got this;
It is giving me the error message "Invalid B-Tree node"
Here is more info on the hard drive;
Name : Hitachi HTS545032B9A300 Media
          Type :           Disk
          Partition Map Scheme :           Master Boot Record
          Disk Identifier :           disk1
          Media Name :           Hitachi HTS545032B9A300 Media
          Media Type :           Generic
          Connection Bus :           USB
          USB Serial Number :           091004B3066D
          Device Tree :           IODeviceTree:/PCI0@0/EHC2@1A,7
          Writable :           Yes
          Ejectable :           Yes
          Location :           External
          Total Capacity :           320.07 GB (320,072,933,376 Bytes)
          Disk Number :           1
          Partition Number :           0
          S.M.A.R.T. Status :           Not Supported
Can someone give me a step by step on how to get the hard drive working again? It would mean the world to me as this footage is priceless and irreplaceable.
OR can you refer me to someone (Geek Squad? Apple Store?) that might be able to help me out?
Thanks in advance!

Answer 1

The error message invalid b-tree node size indicates that the directory on the disk is corrupt. The way that it can be repaired is to reformat as disk utiltiy says.
It is recommended that the data be backed up first before either of this solution are done.
Since it is not be recognized by the sytem at all it does sound like you can back it up now.
Do you have a backup?
If you don't there is every chance you may lose all your data.
You can check to see if a data recovery service can recover any data for you. If you go that route you are looking at spending $$$$
Allan