This has been posted a while ago for people who had the same problem as you, it helped for me.
Guys, after intensively searching the net for a solution to a problem a number of us (including me) experienced where the AV500 stops being recognised properly by Windows, I'm elated to report that I have found a 100% effective and very easy solution, which has just worked for me, and I'm now able to access the device properly again, without having lost any data!
Go here: http://www.cgsecurity.org/wiki/TestDisk
and download a free utility called TestDisk (I downloaded the latest NON-beta version). It's a zipped file, just extract all files to a folder of your choice leaving the option "Use folder names" checked. Then, go to the folder where you unzipped the files, go to the Win folder, and run the testdisk-win.exe file. It runs in a DOS window, even though it says it's a Windows app, but it doesn't really matter at all.
Another note, and just to recap, the problem I was having is that Windows (XP SP2) stopped recognising my device properly. It would show up as a removable drive with a letter assgined to it under Explorer or My Computer, but when double clicking on it, I'd get a message "The drive (letter) is not formatted. Do you want to format it now?". CHKDSK utility under DOS reported the drive was in RAW format, and unsupported. So, I can vouch that if you're having the EXACT same problem, the following procedure will work, otherwise, if your problem is different, use at your own risk, or contact the maker of the software direct for advice, he was very quick in replying to me, and extremely helpful!
So, start the app (you must run it with administrator privileges), wait for it to recognise all the drives, it will take 5-15 seconds. Choose the AV500 drive. Confirm Intel/PC partition. Analyse it. Proceed. Enter to continue. Write on the next menu. Confirm. Quit the app. Disconnect USB cable from the device following the safe hardware removal procedure. Reboot your pc. Re-connect the device and it should be properly recognised, and the whole thing doesn't take longer than a couple of seconds!