Sometimes iPods freeze.  It is bound to happen to you sooner or later.  Maybe you were out jogging and went to turn it off, but it will not shut down.  Or you disconnect it from your computer and it will not go back to the main screen.  Perhaps, you left it charging overnight and when you disconnect it, it will not turn back on.  Instead, you face a black screen, a frozen screen or nothing at all.  Sometimes this is just a glitch, the iPod does not know what to do or gets it programming instructions wrong; other times, this could be indicative of a bigger problem with the hard drive running the little unit.

If your iPod will not turn off, you want to try resetting it.  Simply hold in the Center and Menu buttons until the screen goes black.  From there, it will reboot.  This should fix the issue.  If it does not, or your iPod will not turn on, you want to try connecting it directly to the computer to see if iTunes recognizes it.  If iTunes does not open your iPod or the screen remains black, you may have drained the battery completely.  In this case, you have to charge the iPod via a wall charger to give it enough power to be recognized and additionally charged by the computer.

If your iPod persistently will not turn on or off, there may be a deeper issue going on with the unit.  There could be internal damage to the hard drive or other factors affecting it from properly turning on or off.  Call up Apple and talk to their technical support staff, if under warranty, they will most likely advise you to bring it to your local Apple store or send it in for further testing.  Whenever an iPod issue pops up, take the time to diagnose, test out and try to get it working against.  Ignoring the issue will make things worse over time and could cause more trouble than it is worth.