Have a look here - - -
http://www.techimo.com/forum/t73236.html
had similar problems myself but sorted, finally - - - if this link makes no sense will point you to a 'fuller explanation ' on one of the other forums.
I don't think you want to format if you want to retain the data on there, though in the 'good old days', it was possible to, having formatted and realised you didn't want to, there was an 'unformat' command- - -which, well, un-formatted.