Install the Samsung drivers and utilities. The player is not "synching" correctly with Windows Media Player 10. When Window Media Player 10 "sees" the Samsung correctly, the folder structure of the synching window on the right-hand side will look like the one on the left.
You can actually drag-and-drop music directly onto the Samsung by using File Explorer. Music loaded on the Samsung is put in hidden system files under "MY MUSIC". You can browse this folder by using the "Options" under Windows File Explorer and enabling hidden and system files to be visible. Under file explorer, you can actually move the music files from the wrong "MUSIC" folder to the correct system "MUSIC" folder, as well from your computer. The Samsung is treated by Windows as a mass storage device. Afterwards, use the Samsung utilities to rebuild the database on the YH920.
Make sure your computer hard disk is free from corruption and your music files good, because those can interfere with the synching of any kind of software with any kind of player.