The progress/time bar at top of the screen has disappeared

On my Ipod Touch -- when playing a song -- the bar at the top of the screen (that shows how much total time there is for the song and where the player is within the song) has disappeared. It was there yesterday, and now it's just gone. BTW, the volume control is still there. And otherwise, the player seems to be working fine. Somewhere, I read that this situation might be resolved by re-syncing it. I tried that and it didn't work. Any idea as to what may have happened... and how can I fix it?