Zen Nano 512MB

the song files may have been moved to another folder. from the place you previously synced your file.
you can click on relocate to locate the songs..or sync from the new path...old path will be deleted automatically

You should sync it with Itunes I suspect you have just erased it manually and not through Itunes.Ipods are only compatible with Itunes.

Deleting Files,Pictures,Videos,Audio
Books, Apps,etc. from MP3 Player/Ipod
------------------------------------------------------------------------
Hook up your mp3 player to your computer
Go to your desktop and double left click on "My Computer"
When it opens you will see listing that says "Devices with Removal Storage" your mp3 player should be listed there.
Right click on your mp3 player, and a window will open, right click on "Open" and now your files/songs should be visible.
Hold the left click down and drag it across all the files/songs that you do not want this will highlight the files/songs you do not want, release,right click and then click on "Delete"
Now you mp3 player should be clear of the files/songs you do not want.
BE CAREFUL and do not delete files needed to operate your MP3 player.
This is a FREE answer, Please rate me

Deleting Files,Pictures,Videos,Audio
Books, Apps,etc. from MP3 Player/Ipod
------------------------------------------------------------------------
Hook up your mp3 player to your computer
Go to your desktop and double left click on "My Computer"
When it opens you will see listing that says "Devices with Removal Storage" your mp3 player should be listed there.
Right click on your mp3 player, and a window will open, right click on "Open" and now your files/songs should be visible.
Hold the left click down and drag it across all the files/songs that you do not want this will highlight the files/songs you do not want, release,
right click and then click on "Delete"
Now you mp3 player should be clear of the files/songs you do not want.
BE CAREFUL and do not delete files needed to operate your MP3 player.
Please rate me

try here first and if that doesn't work you should be able to load it using the drag and drop method
support.creative.com/kb/ShowArticle.aspx?sid=14186

heres the drag and drop/windows media player options
**Drag and Drop**
Connect your MP3 player to the computer. Some MP3 players connect directly to a USB port, while others connect to a USB port by way of a specific USB connector that comes with the MP3 player. Open the folder on the computer that contains the music files you want to transfer. This is usually the "My Music" folder, available from the "Start" menu, but it can be any folder where you save your music files. Scroll down to the song you want to transfer to the MP3 player. Right-click on the title. When the options are displayed, click on "Send To." Scroll down the "Send To" options and select your MP3 player. This can be listed as your MP3 player's name or as "Removable Drive." Click on this selection. Continue this process until you have transferred all songs that you want to your MP3 player.
--**Windows Media Player**--
If you have a large playlist to transfer, you may prefer to do it from your media player, such as Windows Media Player. Once your MP3 player is connected to the computer, open Windows Media Player. Click on the "Sync Music" tab. Drag songs that you want from your Windows Media Library over to the "Sync Music" column to create a playlist. Click the "Begin Sync" tab at the bottom once you have all of the songs on your playlist. This action will sync all of the songs to your MP3 player with one click. Disconnect your device once songs have been transferred by clicking on the "Safely Remove Hardware" icon in the bottom-right side of the desktop tray.

Have you tried backing up all the songs and re-formatting the player? This sounds like it could be a filesystem problem...

Or you could check for a firmware upgrade. That's what fixed mine when it wouldn't play mp3s; a new firmware might have a bugfix for your problem. Firmware is available at:

http://support.creative.com/Products/ProductDetails.aspx?catID=213&subCatID=214&prodID=12720&prodName=ZEN%20Nano%20Plus&subCatName=ZEN&CatName=MP3+Players

You Can Download Free MP3 From Youtube By This Site : video2mp3.net
If you didn't found Your Favorite Music In Youtube Try These Sites : Beemp3.com or 4shared.com

upgrade to the lastest firmware
http://193.95.171.83/SRVS/CGI-BIN/WEBCGI.EXE/,/?St=230,E=0000000000295082599,K=2201,Sxi=1,Kb=ww_english_add,VARSET=ws:http://us.creative.com/,Case=obj(12165),Kb=ww_english_add

reboot both.

Have you tried re-formatting it yet? Look at your instruction for how to do this.