My iPod quits playing at the slightest touch of the screen. How can I set it so that music continues playing even if the screen is touched?

My iPod used to allow me to start my music, and then touch the button at the top to turn off the screen - the music would then continue playing until I hit the button again. Now, at the slightest touch of the screen, the music completely shuts off. I've been trying to exercise using my nano, and if my earphone cord even brushes the screen it's shutting the music off!