The computer can only see one mode at a time. In MSC mode, it can’t see the MTP files and vice versa. But the Sansa sees them all.
The Sansa works for every version of Windows, and works in MTP mode with every Windows Media Player version 10 or higher. It’s not tied to Windows XP.
Windows XP originally came with WMP 9, but most people updated to 10 sooner or later.
If you had USB Mode as Auto Detect and had WMP 10, your files were sent over in MTP mode. Now you are connected in MSC mode so the computer can’t see the WMP files.
What happens if you re-enable Windows Media Player, change the USB mode to MTP and connect? Worth a try.
Otherwise go to support.microsoft.com and reinstall Windows Media Player to get the MTP drivers back.
