Windows Media Player may be set to automatically sync with your Sansa.
STEP 1 - Connect the Sansa player in MTP mode to the computer
STEP 2 - Open Windows Media Player
1. Click Start > Programs > Windows Media Player.
2. If you do not see Windows Media Player, click Start > Run, type WMPLAYER, then click OK.
STEP 3 - Edit the sync option of Windows Media Player
Windows Media Player version 10:
1. Click the Sync tab.

2. Click Set up Sync.

3. Click to clear the Synchronize device automatically box, then click OK.

Windows Media Player version 11:
1. Click the Sync tab.
2. On the left pane, navigate to the device. It is usually the last device listed.

3. Right-click on the device and select Set up Sync.

4. Click to clear the Synchronize this device automatically box, then click Finish.
STEP 4 - Format the device
STEP 5 - Load your music files one more time
