Screen frozen, music missing
Performing a hard reset may restore your friend's iPod to working order - doing it should not affect the music loaded onto the iPod. Apple provides instructions for doing this here. From the relevant section:


  
  Toggle the Hold switch on and off. (Slide it to Hold, then turn it off again.)
  Press and hold the Menu and Center (Select) buttons simultaneously until the Apple logo appears, about 6 to 8 seconds. You may need to
  repeat this step.
  
  
  Tip: If you are having difficulty resetting your iPod, set it on a
  flat surface. Make sure the finger pressing the Select button is not
  touching any part of the click wheel. Also make sure that you are
  pressing the Menu button toward the outside of the click wheel, and
  not near the center.
  
  If the above steps did not work, try connecting iPod to a power
  adapter and plug the power adapter into an electrical outlet, or
  connect iPod to your computer. Make sure the computer is turned on and
  isn't set to go to sleep. Try resetting the iPod while it is connected
  to power.