Connection issue where snsa dies and restarts

Sounds like the internal battery needs to be replaced.

Hope this helps. Good Luck!

check whether u have istalled the proper software on ur computer. Or check connecting using a new genuine data cable

go here and download the sansa updater and run it
http://www.sansa.com/download

There are two connection settings in USB: MTP and MSC. For some reason MTP is the default, but it doesn't connect properly on all computers. Select MSC and plug the player in again, the computer will recognize sansa e250 but not show the driver just yet. It is installing recognition software (just basic drivers - nothing heavy) and it doesnt tell you what its doing until its complete. WAIT FOR IT. Once it is complete you will see both the sansa e250 and the removable memory slot in your "my computer" now you're good to go.

There are two connection settings in USB: MTP and MSC. For some reason MTP is the default, but it doesn't connect properly on all computers. Select MSC and plug the player in again, the computer will recognize sansa e250 but not show the driver just yet. It is installing recognition software (just basic drivers - nothing heavy) and it doesnt tell you what its doing until its complete. WAIT FOR IT. Once it is complete you will see both the sansa e250 and the removable memory slot in your "my computer" now you're good to go.

These are the most common methods for recovering Sandisk's Sansa Mp3 Players. I have been almost universally successful in recovering Sansa players using one or a combination of these methods. These methods do not work if you are having synchronization or music format issues - they are for recovering a player that will not power up, freezes, flashes, is not recognized by the computer, and a host of other issues.

Reset the Sansa Player first. On most models, restart is done by holding the power button in for 15 seconds or longer. Check your specific manual to be sure. The manuals are available from the Sansa website if they have been misplaced.
Download the Sansa Recovery Tool from the Sansa website.
Format - Erases Everything: Connect your Sansa player to the computer and open Windows Media Player. Click on the Sync tab. Pull down the drop down menu underneath the Sync tab by moving your cursor over the Sync tab and left clicking on the little black arrow underneath the Sync tab. Highlight "Sansa 1GB" (wording may vary slightly), and then select "Format." - this should erase everything.
Firmware Upgrade- Erases Everything: Get the latest firmware upgrade from Sansa - it updates the firmware and erases every song in the player all at once. Note: this method doesn't work if already have the latest firmware. Go to this website and click "Firmware Updater" to find out: http://www.sandisk.com/DriverDownload/driverList.asp
If these fail, then:
Try this: disconnect the player from the computer, turn it off, hold in the volume + button, and reconnect the player to the computer while holding the volume + button in. Keep holding the volume + button for an additional 5-50 seconds. Windows should eventually go into recovery mode and revive the player- it will pop up a window that says Found New Hardware Wizard.
If you get the problem where MTP Device keeps popping up continuously, uninstall the “MTP Device” by going to Start à Control Panel àSystem à Hardware à Device Manager (you computer may vary slightly, depending on Windows Version).
You may have to restart your computer after each of these methods to get them to work properly. Disconnect your Sansa player BEFORE shutting down your computer.
-Tha Mp3 Doctor

is there a charger (cord plugged into the base) plugged in?

I had the same issue. Brand new Sansa e250 player. My XP SP2 computer would not recognize it. I updated my Windows Media player to version 10. Bingo, all is working now. I previously had version 9. Good luck!

try taking off the back plate and take out the battery then put it back in and turn it on

These are the most common methods for recovering Sandisk's Sansa Mp3 Players. I have been almost universally successful in recovering Sansa players using one or a combination of these methods. These methods do not work if you are having synchronization or music format issues - they are for recovering a player that will not power up, freezes, flashes, is not recognized by the computer, and a host of other issues.

Reset the Sansa Player first. On most models, restart is done by holding the power button in for 15 seconds or longer. Check your specific manual to be sure. The manuals are available from the Sansa website if they have been misplaced.
Download the Sansa Recovery Tool from the Sansa website.
Format - Erases Everything: Connect your Sansa player to the computer and open Windows Media Player. Click on the Sync tab. Pull down the drop down menu underneath the Sync tab by moving your cursor over the Sync tab and left clicking on the little black arrow underneath the Sync tab. Highlight "Sansa 1GB" (wording may vary slightly), and then select "Format." - this should erase everything.
Firmware Upgrade- Erases Everything: Get the latest firmware upgrade from Sansa - it updates the firmware and erases every song in the player all at once. Note: this method doesn't work if already have the latest firmware. Go to this website and click "Firmware Updater" to find out: http://www.sandisk.com/DriverDownload/driverList.asp
If these fail, then:
Try this: disconnect the player from the computer, turn it off, hold in the volume + button, and reconnect the player to the computer while holding the volume + button in. Keep holding the volume + button for an additional 5-50 seconds. Windows should eventually go into recovery mode and revive the player- it will pop up a window that says Found New Hardware Wizard.
If you get the problem where MTP Device keeps popping up continuously, uninstall the “MTP Device” by going to Start à Control Panel àSystem à Hardware à Device Manager (you computer may vary slightly, depending on Windows Version).
You may have to restart your computer after each of these methods to get them to work properly. Disconnect your Sansa player BEFORE shutting down your computer.
-Tha Mp3 Doctor