I had a similar problem myself, the touch pad constantly would scroll down rather than not work at all. I figured out that it was the connection for the touch pad. If you're confident enough you could try opening it up (http://www.anythingbutipod.com/archives/2006/02/how-to-disassemble-the-creative-zen-vision-m.php
) and make sure the ribbon connecting the touch pad is secure.
I've just put mine back together (it happened again on the way home from work last night) so can't really be bothered taking it apart again to show you pictures of what I mean but if you're really stuck I'll take it apart when I have time and post the pictures of what I mean.