SanDisk MP3 Player c250 2 gb

1 Check to see that the player is in MSC mode by going to the USB mode section in the Settings menu.

Step2 Plug the SanDisk Sansa MP3 player into your computer.

Step3 Click on the Start menu.

Step4 Click on My Computer.

Step5 You will now see a drive for the device and one for the SD card.

Step6 Double click on the Sansa device.

Step7 Go to the My Music folder or the location of your music files.

Step8 Choose songs from your folder and drag and drop them to your Sansa device.

I hope that helps..
Please rate accordingly
Thank you
Computerrep

The songs that you are trying to transfer must be in mp3 format.

When you plugged it into Windows, it was formatted as a a FAT32. when your friend plugged it into his Mac, it was reformatted as a non-FAT32. You will have to reformat your player, which will end up erasing all of your songs:
WARNING: The following procedures will erase all songs on the player.

Check if the file system is NTFS. If yes, format it to FAT or FAT32. - Connect player to computer, double-click my computer, right click on icon of mp3 player and select format. This only applies to Windows-based computers.
You can also format the player in Windows Media Player itself:
Connect your Mp3 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 "name of Mp3 player here 1GB" (wording may vary slightly), and then select "Format." - this should erase everything.
-Tha Mp3 Doctor

Songs that are in the correct format will show up in the music menu when you disconnect the mp3 player from the computer. Songs that are in the wrong format will not show up at all when disconnected from the computer.

Open Windows Media Player and click on the icon of the Sansa to view what the songs that have been loaded onto there.

when using a mac, u have to make sure the player is in msc. then you can drag music directly to it.

There can be a number of causes, if you are a Mac user and you don't use a clean eject app/script some of the hidden Apple cataloguing files can cause this issue. 
Songs in the wrong file format such as AAC or OGG can also cause this issue as can some firmware versions.
Start by making sure all the songs on the player are in a supported format, for most versions of this player that means MP3 and/or WMA, however this player has been released under several brand names in several markets and one or two versions don't support WMA.
Also, if you are a Mac user, use a clean eject app such as FinderCleaner, it's even supplied with an Automator workflow so you can create a menu item and/or folder action for it. 

ive had this same problemo. you cant use the media converter to drag and drop songs. you have to download your songs or rip them onto windows media player. you plug in the sansa and then when its recognized there will be an area on the right hand side where you drag the songs and they appear on sansa.

Reformat the player

First switch your USB control to MSC. Then turn off your mp3 player and activate the hold icon. Then turn it on while holding the record button with hold icon still being activated. then it will go to recovery mode. Now plug your sandisk into the computer and wait until it says RECOVERY COMPLETE...PLEASE DISCONNECT or when it just says for you to disconnect. This worked on my sandisk, and it hopefully work for you.

take out battery for a few seconds. replace it and turn on player. make sure battery has good charge in icon. transfer songs again. in realplayer make sure to hit the "eject device" button. DO NOT DO ANYTHING UNTIL PLAYER RETURNS TO NORMAL OPERATION it needs to place all in memory. goof luck