try to remove the battery, wait 30 seconds and replace it
this should reset your sansa,
a real hard reset isn't possible,
you can format it though
warning, this removes everything
To format your Sansa E200 series MP3 player:
1. Open "My Computer."
2. With the player plugged into the USB port, right-click on the
player (if in MTP mode) or the drive letter for your player (if in MSC
mode) and select "Format" from the right-click menu.
3. Press "Start."
4. You will receive a warning that the format process will erase all data on your device.
IMPORTANT: Make sure you have backed up all of your data from the
device before continuing with the format. Procedure will erase
everything off the player. Agree to the warning.
5. The format will complete. Close the format window and your player should be ready to use.
After the format, please install the latest firmware update for
your player. Please visit the following link to download and upload the
Firmware on your Sansa E200:
PLEASE NOTE: All files will be deleted. Backup your files. Your MP3
player must be in MSC mode before installing the Firmware update.
To set your player in MSC mode, please do the following:
1. When the player is turned on, press the “Menu” button.
2. Navigate to the “Settings” menu.
3. Navigate to “USB”.
4. Under the “USB” menu, go to “MSC”.
After changing the player to MSC mode, reconnect it to your
computer. The screen on the MP3 player should read “USB Connected”
You can now complete the Firmware update download from SanDisk.com on your device.
1. Unplug any other USB flash drives that's connected to any of your USB ports.
2. Download the firmware to your PC
3. Plug in your e200
4. Double-click on the downloaded firmware (e200fw01.00.12.exe) and follow instructions
5. Unplug your e200
6. Device will do it's own update process and will restart.
The device should be ready to be used again.