Flashdrive help

Hello,
hi i have a 16gb flash drive and when i first got it i was able to open it and i put a doc file on it but when i went to open it again i was asked to format it so i tryed to but my windows xp and my windows vista laptops keeps telling me that ( windows was unable to complete the format ) so what do i do now??????????. I do hope that someone can help me because this is driving me nuts.I hope to hear back from who ever gets this.thank you.