depends how much you know
first is the disc spinning?
can you see the disc in your file manager
can you see any files at all?
it sounds like the file table is damaged (fat, fat32 or ntfs) - what os you using 'cause ntfs is normally quite resillient?
occasionally a file recovery prog will do the trick .... but they generally work by reading the table .... so if it's gone ... so have your chances
If you know how ... a hex editor (win hex) will allow you to do this .... but it's quite skilled
if the files are valuable .... you can pay a data recovery firm to do the job (approx �70.00) most work on no joy - no pay.
when this is over ... log on to the mfr's website and download their disc utility and you might salvage the disc .... but it's totally destructive ... so beware