depends on what you did and on what you did after the goof.
if you have not messed with the drive and if it was a file delete you can find undlete programs that can find the files and restore them.
or if it's worse there are programs that can search a drive and try to recover the whole drive file by file.
or you can pay a company that does that stuff to do it but they ared not cheap.
but if you have been run ning programs on that drive and wrote any changes to it then you are less likely to get the files back.
every write means less can be found.
formating a drive make sit harder but not totaly impossible to get old files, but more difficult and costly.