Hi,
I think it is not that strange...
Pure theory:
A certain hickup in the hardware screwed up the CPU (CPU internal hang up).
The battery was already below the lowest power to start the device but
delivers enough voltage to keep the (wrongly populated) internal registers
of the CPU alive: The confused state of the CPU remains and locks itself
off from the "real and healthy world".
After a night of doing nothing other than draining the battery a little more,
the voltage falls below the point the CPU keep their confused registers.
Everything goes back to zero, init, start or whatever.
Attaching power in the mornig was like a cup of fresh coffee for that little
device because the CPU now was able to start right from a blank sheet.
Voila!
I think some of the "totally bricked devices" could be taken back to
live to desolder the battery for a night or so to discharge anything
and to give the CPU a really really fresh reset without remembrance
of its confused past.
WARNING!
Pure theory extracted from the experience with other embedded devices.
I do not even own a Sansa player (but hope to do it soon...

WARNING!
Fingers crossed...
Best regards,
mcc