This forum might be a bit general to get the answers that you are looking for. You might get the answers at http://www.sansa.com/
Thay have forums there on each of the players that they have.
Hope this is of some help.
I've had my Sansa 250R for about 2 years. I lost it for half a year and just recently found it.
For some reason my main computer will not recognize it as a MP3 Player, let alone anything else (if it is recognized it is a storage device) The same thing goes for my friend's newer Sansa 250 model. But, for some reason they will both be recognized on his computer. The player works fine other than this problem.
I have looked for solutions for the past week or so and have come up with nothing. What I have tried includes: switching from MTP mode to MSC mode, reinstalling Windows Media Player 11, and updating the device's firmwire.
The Sansa 250R is a rather old model, at least as far as I can see. But if you have any ideas that may help me or others with the problem, I would most appreciate it.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic