Windows 7 - recover pen drive data

Hi,
i have a 4 gb pen drive, with very important data in it. But suddenly i got a message that ''it need to be formatted before use''.
i understand that pen drive is corrupted, i tried to recover data by many softwares but they cannot recognize the partition as well.
I thought that a format might be solve that issue....
But after format pen drive works and data cannot be seen/recover by any software at all.
I again say that it contains very important data and i dont want to loss it, so kindly show me a way plssssssssss.............

You could try an "unformat" utility. Did you by any chance change the format to/from NTFS and FAT32 with a quick format? I did that on one of mine and it lost data even though there was nothing wrong with it. Those drives are not for permanent important data. It's more like convenience. The electrical connections going in and out of those little chips get funky and your data is gone. Not reliable. In fact I'd trust an old 3 1/2" floppy diskette over a USB pen drive... at least for the first couple of months.

Did you try recuva?
Recuva - Undelete, Unerase, File and Disk Recovery - Free Download

what is your file system format ??
you can try ntfs undelete, if you use NTFS format.
it's free..