I had this problem, too. I’m no expert, but I think you’ve done what I did - inadvertently ‘bricked’ your device - so it isn’t being recognised as an mp3 device anymore. I finally got mine ‘back’ after I asked my husband for help and he installed the firmware from his laptop, which runs XP - mine runs Windows 7 and I had had no luck at all. That business of holding in the volume button while plugging it in, is very hit-and-miss, and it was, even on the XP machine, but it did finally work. We also cut a strip off an old credit card and pushed that gently into the memory card slot of the device (not sure whether that did anything, but we read that on another thread). The one thing that I think made a difference was doing a hard reset on the device before installing the firmware from the XP machine (this from the user manual): To perform hardware reset on the Sansa Express™ device, press and hold the Select button while pressing the Volume Up (+) buttons simultaneously.
Also, take a look at this thread, which is about the same topic: http://forums.sandisk.com/t5/All-other-MP3-players/Sansa-Express/m-p/225976#M16008 and suggests that the firmware updater doesn’t work properly with Windows 7. Good luck!
