hey i just registered to say that i may have cured my own m250 of the freezing problem that seems pretty common. The problem I experienced was that it froze while rebuilding the library and then would never get past the sansa screen nor would it mount on a computer. I just did it today so who knows how long it’ll stay fixed, but it might be worth a shot If yours isn’t under warranty anymore.
What I did first was remove the case (take the battery and the one tiny screw out and gently pry apart the two sides). On what would be the right-hand side of the player on the side opposite the screen there’s what looks like a small second tier of circuitboard (I assume it’s the memory chip) that comes out pretty easily if you pry up from the bottom. Loosen it a bit, but leave it connected. If you hold the battery in place and turn it on, then remove this chip the screen will change, saying there’s no memory, and if you then replace it, the screen will say no files and shows the battery icon.
So what I did was turn it off and plug it into my computer, where it sticks on the initializing screen. I did the same thing here: pull off that chip and then replace it, which actually got it to mount so you can format it (all my files were still on it, fyi). It’ll probably end up with the same problem again, but hopefully it’ll last a little while like this.