Not enough memory space for music db
Your M240 may have encountered a corruption in its Music Database, and may be corrected by formatting and updating the firmware.
Try this: Manually switch the player to MSC mode and format through "Disk Management".
Here are the steps:
Locate the "Hold" switch on the side of the M240 and enable it (you should see an "orange-colored" surface when it's enabled)
Plug the M240 to your computer (recommended Operating System is Windows XP and above) and check Windows Explorer if the player is detected as a "Removable Drive"
Open "Disk Management" by right-clicking on the "My Computer" icon, then selecting "Manage"
Your "Disk Management" window should be divided into 2 panes. On the left pane, click on "Disk Management"
On the upper right pane of "Disk Management", you should find the drive letter corresponding to your Sansa M240. The lower section also contains the drive # pertaining to your M240. Right-click on either drive letters pertaining to the M240 and select "Format". Follow the on-screen prompts. Make sure that the "Quick Format" checkbox remains un-checked.
In general, Disk Management is more the effective tool for formatting your M240 and assuming the format processing completed without any errors, proceed to updating the firmware of your player.
Use this link to download the Sansa Firmware updater:
Save this file to your Desktop and run it while your M240 is still plugged in to your PC. Follow the on-screen prompts.
"Safely remove" your M240 from your PC and -- with a fresh battery -- power on your player. It should boot up normally.
I hope this works. The M240 is a great player