Note (May 2010): Since this was written, the firmware link to Sandisk.com died, and you may be better served using their new updater application. However, if you have a "version 1" e250 and you want to give this a try (at your own risk of course), I've placed the firmware that I used at the bottom of the article.
SanDisk doesn't publish the steps to accessing the recovery mode on the e250 flash player. So when mine had some filesystem corruption, I eventually ended up with a device that would not boot. It went into database refresh mode, and stopped partway through, frozen.
Initially SanDisk suggested I format the drive from Windows, but since it wouldn't boot, I could not mount it. (Good to know, though, that the drive can simply be formatted without ill effects.)
Please hold down the power button for 20 seconds in order to soft reset the player.
If that fails to resolve the issue then we may need to format your device. Please connect the unit to your computer, go to my computer, right click on the removable drive associated to your player and select format. This will erase all data off the unit and correct errors from it; making the unit usable again. Before clicking on start make sure that the file system is on "FAT32" and that the format options are all unchecked.
Please know that you need to back up your important files first by transfering them from your device to your computer as formating will permanently erase all the data from your device.
Anyway, that didn't help me with my problem, because mine would not even boot to be mounted.
The second suggestion was much more interesting!
Let us try to put the player in recovery mode. Please turn the player off (hold the power button down for 20 seconds if you have to), then put the hold switch ON. Now hold the record button while you connect it to the computer, keep holding it until it finishes installing the new device. Now attempt to do the firmware update again.
The firmware update he mentioned is here. [Note: dead link. See below]
This did the trick for me, although I actually had to do it twice.
So I'm posting this for anyone else who may be having a similar problem, and wants to reset their player to factory defaults. It's worth noting that I was pleased with SanDisk support. There was a decent turnaround by their support system, each response was less than eight hours in coming after my request message went off.
One last note: This is the only Sansa player I have, but it's possible that the above procedures will work with an e230, e240, e260, or e270. Of course, please try it at your own risk. :)
Below is the firmware I downloaded for this article. Please, don't use this unless you're sure you know what you're doing. I highly recommend you use Sandisk's normal updater instead.