HELP!!!! my Sansa e250 2gig... HELP! please!

[Just go Play]

I am not familiar with this mp3 player but if it has [A] flash memory and the file system is formatted as [B] fat16, [C] you use windows media player or some other app to sync files and [D] you have lots of folders most likely you have exceeded the limits of the file system.

If running chkdsk as Brian suggested then you can try reformatting the drive

From a command prompt ( START > RUN type CMD click OK)
type format driveletter: /Q /X
With any luck you now have a clean drive and can reload your mp's.