Ok have now fixed the disk and all seems ok. So data wasnt killed fortunately.
For reference this was what i did.
Suspected cause: symptoms suggested partition table possibly damaged.
Steps taken to fix:
Downloaded Partition Table Doctor 3.5
Used the dropdown list to select the faulty disc (this was a data disk not the boot disk)
Clicking the browse button revealed that the data folders were still visible (good sign)
Selected option to rebuild partition table.
Rebooted PC
Disk now visible and working correctly again.
Thanks for your help guys.