In MSC mode, I cannot see any music files/folders when the Sansa is connected to the computer. Please advise.
There is an issue with the USB mode: a computer only can see the files that had been transferred to the player under the mode that the Clip then is connected to the player under. And so for ease, best to stick to one USB mode.
To “fix” matters: connect to the computer with the USB setting set to one USB mode, transfer the files you see to your computer, delete those files from the Clip, disconnect the player, set the player to the other USB mode, connect to the computer, and transfer the songs on your PC back to your Clip. And then keep the player set to that USB mode.
Personally, unless you have DRM’ed files, I’d recommend to stick with MSC USB mode. Whatever you do, stay away from the Auto USB mode, which can switch (silently) between MSC and MTP modes.