Issues with USB drive

Hi have a 32gb HP USB stick that I use for all my work data and although I try to back it up every month I have been overwhelmed with demands and failed to back it for the past 5 months. It was working just fine and one day last week I plugged it in to do some work and it did not open normally. I went to My Computer and saw the drive, double clicked on it to open it and got an error stating the drive was not formatted, did I want to format. I of course selected NO. I tried the stick on multiple other PC's with XP Pro which is the main OS I have been using and I tried it on a Vista and Windows 7 OS but still no joy. Get the same error every time.
I ran into this once before several years ago and was able to recover all the data but cannot recall what had to be done. I really need to recover the data as there is months of critical data and work on it.
Any suggestions are welcomed.