Take a look here.
http://www.pcbuyerbeware.co.uk/Tips.htm#probleminst
Scroll to " How things can go wrong with a USB Device".
"KiwiBrian" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> I have a 128MB USB FlashDrive which is recognized by my XP Pro when I plug
> it in, but a few seconds later it disappears from the Windows Explorer
left
> hand pane.
> When it is shown it is not displaying any name or drive letter.
> If I then go into Computer Management, it is shown both in the USB area of
> the Device Manager, and in the Disk Management area, where it is given an
> appropriate Drive Letter.
> If I then change the drive letter to another free one, it will be shown in
> Windows Explorer and I can use it.
> However if I unplug it from the USB channel this process reverts back to
> disappearing mode again.
> I have used it successfully for several months before this started.
> A possible clue is that I did install a pseudo-drive using Daemon, but
have
> since deleted that.
> Any help would be appreciated.
> Brian Tozer
>
>