Sansa m250

just hold the button power for about 2 minutes dont let it go till it turns off. when it's of u can restart ..it works believe me

I have the same problem. I took the battery out overnight and the next day it was working. This is the information I got from Sandisk.
Before we suggest any changes in the player's software or memory, let us first check if this is a power issue. In order to remedy this problem, we might need to do some power cycling. In the case of a frozen or hung device, power cycling refers to turning the device's power off and then on in order to get the device to function again. Let us power cycle by doing the following:

1. Take the battery out of the player.
2. While the battery is out, plug the player into a computer's rear USB port.
3. If the screen is blank, try a different USB port. If the computer is a laptop, try this procedure on a desktop before moving on to the next step.
4. If the screen reads ?USB Connected? when the player is plugged in with no battery, unplug the player.
5. Hold the power-on button for 45 seconds (Please perform even if there seems to be no reaction from the player when connected to the computer).
6. Connect it to the computer again (still without the battery).
7. If the screen once again reads ?USB Connected,? disconnect the player and insert a new battery which has never been previously used.
8. Try powering on the device.
9. If it still will not work, repeat the process and leave the battery off the player for 1 hour before powering on the device.
10. If none of these procedures are successful, try to update your firmware.

Note: Firmware updates are coded instructions that can be written into the program memory chips of the device itself to improve or correct how the device performs certain functions. Refer to the following link, read the instructions there, and apply the latest firmware update:

http://www.sandisk.com/Retail/Default.as...

Note: The player is only supported on Windows XP. We do not recommend the usage of the player on any other operating system. If the player is not recognized, try it on another computer.

At this point, it is best to format the player to see if this is caused by file corruption. Formatting will erase everything on the player, therefore, before doing so, it would be a good idea if we back up all the files that is on the player.

1. Open "My Computer" and right click on the "Removable Drive" that pertains to your Sansa.
2. On the drop down list that appears, choose "Format."
3. On the "File System" drop down list, make sure that "FAT" is highlighted.
4. Click "Start."

Once formatted, the player will immediately be rid of any corruption and should be usable once more. At this point, it is best that you apply the latest firmware for your player.

Call Sandisk Support and get an authorization and return shipping label. Its seems they are all defective.