I believe most of the models start with "NWZ." Probably the library file was corrupted. The music is still there, but if there is something wrong with that library file, then you won't be able to play your music, as you have found. The best thing to do is start over.
Try formatting the player, but DO NOT do it through your computer. Do it on the player itself. Go to settings. If it has a screen, then it should be the lower left icon that kind of looks like a tool box. Then select common settings, then format. You may have to go down the list if your screen isn't large enough for it to show. It should be on the list beneath "reset all settings." Formatting should delete everything that is on it, including the corrupted library file.
Try syncing with Windows Media Player again. If you're still having problems, you may want to format again (remember do this on the player itself and not through your computer). Then instead of using WMP, you could either employ the drag and drop method using Windows Explorer or try an alternate media player that will work with it(Rhapsody, Media Monkey, etc).
I was putting my music on my walkman, when it said that there was an error. Now, when i go onto music it says "library encountered error, no songs available for playback" When I try and sync music on in says "windows media player encountered a problem when syncronizhing the file to the device, click web help for more information" but when i do, nothing happens.
Nothing is working, please help!