4gb moserbear needed 4 pendrive

hi there
i have a 4gb moserbear pen drive. I have been using it from last 3-4 months & saved some of my very important documents & pictures in it. It was working all fine. But just a day ago when i plug it in a dialogue box appear which says you need 2 format the disk in drive G: before u can use it & asks me if I want to format it-when I click "no" I can't access the drive.I m afraid if I format it won't I lose all my files? The drive properties show 0kb for free space and 0kb for used space. Plz tell me some solution so that i can access my pen drive without losing the data in it. Cuz there is some files which i have saved there only & not on my computer. I use windows-7. Plz tell me some soln