First thing's first, you're going to have to reset the iPod by holding down 'Menu' and the 'Select Button,' then switch the hold switch so that the default Apple OS loads.
In order to fix your problem, a suggestion is to use a 'Noscaling' build (depending on your iPod), or use another unsupported build such as those made by Senab or Pijulius. This problem has existed since the 01/14/07 build, and I'm not sure when it will be fixed, but for now use an alternative.