Songs play on computer, but not sansa

I just bought a sansa clip 1gb. I read the directions of the device and followed the instructions. When the music was done copying into the music folder, I disconnected the USB correctly (with the safely remove hardware icon). After it was disconnected I went to listen to music but there is only the factory stock songs on it. I plugged it into my mom’s computer to see if the songs had even taken to the sansa clip, and they were all there and playable in windows media. Why are my downloaded songs not showing up on the sansa screen? They’re there, but not showing up! Help me please!!!:cry:

Its likely the songs are not in a supported format.  You need to have songs in .wma or .mp3 format to be playable on the clip.