any idea how to un-format?, im guessing the origional files are ok and its the copy over process is whats guffed up
ive just ran a recovery but thats not found any nef files which is what im missing it found some old jpegs i did when i got the camera, but i dont want to recover those in fear of loosing everything else..
If you think it is a transfer communication problem, then try transfer again, in other ways. Different USB ports, a different card reader, a different computer, etc. No repair on the card would help that.
Assuming Windows, and that the card is currently for example computer drive letter E:, then:
chkdsk E: will check and report errors on the card.
Or then, chkdsk E: /F can attempt to repair it, and can fix some issues, but can also lose some corrupted data trying. It puts the data it knows it loses into other hidden files on the disk. If plain text data (recognizable to the eye), recovery to some extent might be possible, but generally its gone.
Another format will simply replace the FAT with all blank entries, i.e., all your data is lost.
But reformat (in the camera) is the simplest and best way to clear your card to be empty (each time after you successfully transfer your images). It is Good to take time to check your image transfer is OK before you format the card again.
In the case of a memory card, a new card is probably the correct action if chkdsk reports much error. Chkdsk is for hard drives, where simple replacement is a less feasible choice. However, chkdsk also has to communicate with the card in the same way data transfer accesses it.
How FAT works:
The disk device (the memory card) has a small FAT area at the top (File Allocation Table). This is a small table (an entry for each file present) that has the file name, all the various dates, the file size, attributes like Hidden or Read Only, and the location where the file data begins on the disk. Each disk cluster of data has a pointer to where the next cluster is located. If you see the impossible 7GB, this is very much corrupted. FAT32 is 32 bits which holds numbers (a cluster count) up to 4GB files, but simply cannot store a 7GB number. 7GB means something is bad wrong. NTFS in the computer can hold larger files, but the card is FAT32.
Recovering old JPG files would not have any adverse effect (and would not help anything about this problem).
When one file is deleted, the only change is that the first letter of the file name is replaced with a tilde ~. This means deleted, and it becomes invisible, however nothing is deleted. Its space (FAT table and the file space) is declared free and available, and some new file can be written over it, but until then, there are utilities that can recover it (simple undelete), by searching for the tildes and then "reading" it, if not yet written over. Undelete utilities have to ask you for the real first letter of the file name.
Probably not helpful here, but FWIW, see
https://technet.microsoft.com/en-us/library/cc938438.aspx for some FAT details.
When we reformat a card, the FAT table is simply cleared, all zeros... which declares the entire card is now available - no files on it now. But nothing else happens, the data is not affected (by a simple format... but low level format writes zeros over all of it), and rather sophisticated tools might still recover some of it (until overwritten with new files). But not if it is corrupted.