Data convert into small size

i have a large amount of data in my pen drive.
some days ago my pen drive was not opening. i tired several time but did not get success.
my friend run a command in cmd

chkdsk /f

and after some time i was able to open my pen drive.
but when i opened my pen drive, i saw that the file which was more than 500 MB, showing only 8 KB and it happened with all files.
there was only 10 MB free before this command run by my friend and still it is showing 10 MB free while all files has converted into very small size.
i have already tried with show hidden files but not got success.

so Please help me to recover my data as it was.
is there any method to get all my data?




Regards
Janardan Singh