some useful discussion:
http://www.pinoymac.org/forum/viewtopic.php?p=395
the bits that may be applicable to your case:
".... Anyway... the MENU and PLAY combo fixes most problems, but there are a few rare case (one in a million... and i was one of them) where the iPod doesnt boot past the Apple logo.
In this case, you'll need to put your ipod into disk mode, so that you can reconstruct your iPod's directory block (which in this case would be damaged if you get this symptom). To force disk mode, press the PREVIOUS and NEXT buttons for 5 seconds immediately after resetting the ipod (MENU and PLAY buttons). You should get a "OK to Disconnect" messages with a big checkmark across your screen.
In some cases, at this point you can reset the iPod and it'll work normally, but most likely you'll have to run Norton Untilites and then connect the iPod so that you can successfully restore your iPod's directory (do NOT initialise the iPod unless you want to loose everything)..... "