surely there could be a different reason for the sad face - but to be honest - i always had ipods with a faulty hard drive - the "low battery" message will disappear after you replaced the hdd.
there are 2 "regular" hard drive problems
1, the drive is clicking
2, you cant hear anything from the drive after you switched on the ipod.
if it's clicking - you could try the "smack your ipod" "fix"
if there is no spinning at all - well, i gues it simply died
but if it's spinning, you could also try to boot into "diagnostics board"
check IO/HDSpecs - i guess that the hdd will show only crappy data - like a hdd size over 90gb for a 30gb drive