I had a similar experience with my Fuze....I found that be resetting it (holding the on button up for more then 10 seconds) the sansa was reset and good to go again...Hopefully, by now you have long since resolved the issue for yourself.....

If your battery goes totally dead, you have to force the player into MSC mode. Turn the player off. Click the button on the right hand side into the lock position (down, orange color will show next to button). Then hold |<< on the the front and keep pressing while you connect the player to your computer. You will see the charging signal next to the battery indicator. It takes 3 hours to fully charge. Good luck!

I am having similar problems. The Fuze seems to have become very sensitive to being moved while it is playing! It shuts off and then I have to dump the power like above. However, it is happening every hour...or so. I have been listening to audio books while doing dull work. I listened this afternoon for about 2 1/2 hours and it quit on me twice. Is there a replacable battery or something that may need a change out? I also do not get an indication of low battery however. I get to a good part of the book and out it goes, then I have to refresh media, etc., it takes several minutes to get going again.
Any ideas?