Cannot use my flash drive

I have a 4 gb flash drive that I can't use. Windows recognizes it but when I click on it, a message shows up telling me that my drive needs to be formatted. And believe me there is no way it can be not formatted because I have more than 2 gb of information in it. To raise the level of my fear a little higher, when I press on the Yes button authorizing the computer to format it, a message pop up telling me that my drive cannot be formatted. So now, I cannot see or open anything in it, I don't know what to do. Any help will be appreciated.