There's good news, and bad news. The Good; hopefully it's only the one partition that's damaged. The Bad; I hope you had a backup of that partition.
Unless you want to go the, possibly expensive, route of paying for data recovery, consider the data lost.
To get things going again:
Select the 1 TB WD entry on the left.
Run Repair Disk on the First Aid tab to check that the Partition Map is ok.
Assuming that it is ok, select the disk2s3 entry.
On the Erase tab, click Security Options.
Move the slider one notch right, so that it says Zero Out Data
Rename your disk and click Erase to create a new volume.
This will take some time, as it needs to write to every sector of the partition. This will also help to map out any bad blocks that may have caused your problem in the first place.
Be aware that if there is a hardware problem, your disk may show additional issues. Keep a backup of any data you store on it.