If you have a V1 player (denoted by just having E2xx not ExxV2) then you can try to place the player into recovery mode and reflash the firmware. To do this, follow these steps:
1: With the player off (press and hold the power button for 30 seconds if you're unsure) activate the hold switch by sliding the switch at the top of the player towards the headphone jack so that you see orange.
2: Press and hold the record button on the left hand side and connect to the computer (KEEP RECORD HELD DOWN)
3: Watch the screen of the player, it should be DOS looking writing on it, once you see Welcome to Recovery Mode on the player you may let go of the record button
4: Open your My Computer Icon and you should see a folder/icon that says "16MB Format". Open this and you should only see one file at the moment, it will say Version.txt
5: Now you'll need to download the manual firmware update. (Ensure that your player doesn't have a "R" at the end of it) as that would need a different firmware. *NOTE: There is a difference between E200 and E200R and E200V2.
If its an E200, click here
If its an E200R, click here

 Download the firmware and unzip/extract the files. Once the files are extracted, copy them and then paste them into the 16MB Format folder where the Version.txt is.

Once the files have been pasted in this folder, disconnect the player and watch its screen. It should say something along the lines of "Reading main image, writing main image, time taken...."

It'll restart and give you a keylock error. Remove the holdswich and try to boot up.

If you don't see any txt on the screen of the player, try again as it may not have been done correctly.

If it does the update but still fails to boot, you may want to remove the battery, press and hold the power button for 60seconds then reseat the battery and try to power it on. If that fails, if the player is less than 1year old, then just call SanDisk and they should be able to create a RMA. If it's older than that, let me know and we can try one last thing.. it'll require pictures (by me) 

It will probably be an RMA then, as the techies are gonna have you do the above

Try removing the battery. Press and hold power (without the battery) for 30 seconds. Once done, put the battery back in, and try to charge it. If that doesn't work, you may need to place the device in recovery mode and create the Sansa.fmt file.. I know i made a walkthrough somewhere... I'll post a follow-up when i find it

"Error! Application Failed to Read Version Details". Also if you can find the proper software to the Sansa E250 edition, can you please give a URL? that may be the problem. Thnx much appreciated...

Hybrid, the Error reading version details, means (normally) that either its the wrong version of firmware being loaded (i.e V1 for a V2 or vice versa) OR that the version.txt file is corrupt, in which case you'd need to have the Sansa.fmt file wipe the player (Format).
Buck, the key lock should just be indicating the Hold switch is on. Try reloading the firmware with the above steps, and before disconnecting, dis-engage the hold switch.. sometimes that bugs the player when updating/reloading the firmware.
If that doesn't work, a Sansa.fmt file will need to be created, that wipes the White Screen of Death effect out about 90 percent of the time. Let me know if the reload still doesn't help

Apix said: Hybrid, the Error reading version details, means (normally) that either its the wrong version of firmware being loaded (i.e V1 for a V2 or vice versa) OR that the version.txt file is corrupt, in which case you'd need to have the Sansa.fmt file wipe the player (Format). Buck, the key lock should just be indicating the Hold switch is on. Try reloading the firmware with the above steps, and before disconnecting, dis-engage the hold switch.. sometimes that bugs the player when updating/reloading the firmware. If that doesn't work, a Sansa.fmt file will need to be created, that wipes the White Screen of Death effect out about 90 percent of the time. Let me know if the reload still doesn't help

Followed the instructions, unlocked the hold before removing the usb, the player reset fine with the normal menu screen, but as soon as I turn it off then on , or hook it back to the computer, it goes back to the SanDisk boot, stayes on for 5 seconds, the screen turns white for a second, and it reboots back to the SanDisk, does this over and over again till i force a shutdown by holding the power button for 20 seconds . Thanks so much for your help.

Hello everybody!
I have kind of a same problem as olive56.
My girlfriend owns a sansa e250 player and everything worked just fine 'till she wanted me to put hebrew interface on her player (I'm from Israel).
After this there were some bugs but they were minor and the player still worked.
Some time went on the first dying signs appeared. First, it started freezing when it wanted.
Now, I have a bigger problem.
My girlfriend turned on the player on her way home and it stuck on the boot screen and she couldn't turn it off untill the battery went low.
When I try to run the player without connecting it to the computer it always shutsdown 'cause of the low battery.
When I connect it to the computer it stuck on the boot screen and nothing happens.
I tried to remove the battery as was said above but it didn't help. I also read somewhere that it may be because of a MicroSD card bug with the player and I found a MicroSD which I inserted into the player but again, it didn't help.
Next I tried Apix's instructions and followed all the steps but it didn't really went as he described.
The first strange thing was when I held the record button down and connected the player to the PC.
Instead of getting the message about recovery mode I got the next one:
Mini-B->Device Mode
USB2.0 MSD
I've downloaded the files apix provided for e200 and extracted the files as he said (to the 16mb-format...)
At that point when I disconnected the player from the usb instead of getting a message about reading a main image... I get:
Upgrade finished
Resetting the system and then I get a message about low battery and the player goes down.
When I turn it on it shows me a picture of a lock but I dont see any text. When I turn hold off and try to run the player it stucks on the boot screen.
Don't know what to do... help me guys =\

I can not find the file now . But had the same problem and googled and found a program that had me put mine in recovery mode and fixed it right up

If your player is freezing or lagging on the refresh database screen, you'll need to create the Sansa.fmt file to do a root level format to your player (different than a format through the computer). *Note this will erase ALL your data on the player.

You can use the picture tutorial for step by step instructions. The only missing steps to this is you first need to open up Notepad. You can either do this by going to the Start menu or by Right Clicking in a blank space of the 16MB Format folder that you see once you place the player in recovery mode, select New, then Word Document.

To place the player in recovery mode:
Make sure the player is FULLY powered off
Activate the hold switch so that the orange indicator is showing
Press and hold the record button
With Rec held down, connect the player to the computer. You should see a black screen resembling a doss screen and it will say

Hey, I have tried the method above but it does not work.
I am desperate now and was wondering how the one below works.

'If your player is freezing or lagging on the refresh database screen, you'll need to create the Sansa.fmt file to do a root level format to your player (different than a format through the computer). *Note this will erase ALL your data on the player.

You can use the picture tutorial for step by step instructions. The only missing steps to this is you first need to open up Notepad. You can either do this by going to the Start menu or by Right Clicking in a blank space of the 16MB Format folder that you see once you place the player in recovery mode, select New, then Word Document.

To place the player in recovery mode:
Make sure the player is FULLY powered off
Activate the hold switch so that the orange indicator is showing
Press and hold the record button
With Rec held down, connect the player to the computer. You should see a black screen resembling a doss screen and it will say'

Could someone please teach me?

Really appreciate it! Thanks.

your info above is thorough and helpful, however I performed each task above and the problem persists. I have a two year old monsta e200r. I erased the music today and replaced it, no problem until it went to the refresh database screen and after 2 minutes or so of slow progress (perhaps 15%) an ominous scintilating blue screen appears, the blue ring remains illuminated until I hold the power button for 15 seconds. I've gone to the MSD mode multiple times and updated firmware and even removed the battery etc. On one occasion it did come up without going through refresh mode and appeared to work except it perceived no music (although through the media player the files are detected though not displayed) any advice would be helpful

I have a Sansa E250 that my Girlfriend bought off ebay for $20 that she hasn't gotten to work since day1 and understood it may not work. I tried the solutions on this page and nothing worked. Not even the sansa updater worked for me. I would just get the message

If my sansa e280 freezes on me..( which is often does ) i just remove the battery, put it back, and turn the power on..WORKS all the time..