Have you to reboot it. Menu + select to reboot it. If nothing else works, check the hold button, make sure it's not in hold. can you get in disk mode (select+play) and/or diagnostic mode by pushing rewind+select? The last time that happened to me on a 4th generation is was the logic board that froze and after I replaced it no more problems. Of course that does not mean that what it is in your case, so you will really have to check each part. The hard drive is also known to give errors like that. Is your ipod recognized by iTunes and/or your computer?
1. Toggle the Hold switch on and off. (Slide it to Hold, then turn it off again.)
2. 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.
Just had similar issues with a 4th gen iPod, needed a new click wheel an replaced the HDD cable, now it works :-) who knows it may work for you too.
good luck and let us know how it is going.