Kingston mass storage needs formatting again

Hello, I purchased a Kingston Mass Storage USB drive (8 g) and the problem is that you cannot retrieve the information after you save more information into it. Let's say you successfully downloaded 10 files into it, and they're there, and you're able to use them and tha's fine. So far, no problem. Then, you decide to add more files (I've seen this happen specially with mp3 and video files) and it will let you save them into it. But then you want to access them from another computer (or the same computer you used to make the last modifications into it) it will tell you that the USB drive doesn't have a format, so you have to format it (and lose all the information) and there's no way around it (even going back to the PC you used to make the changes won't give you a choice). Has anyone experienced a similar problem? How can it be fixed? Thanks a lot in advance.