iPod doesnt show songs, iTunes and Explorer does
First, remove all songs from the device (from within iTunes) and then try re-adding them. If that fails to have any effect, remove all songs, unplug the iPod, re-plug, and add a few back. (Don't bother checking for songs in Explorer; that's not going to help.)

If that doesn't work, back up any data that has made it to your iPod and restore the firmware in iTunes. Then try to add a single song and see if that works. (Add a playlist with one song, then try dragging one over manually, if you prefer that setting.)

Comment on what worked or didn't: if nothing works, I'll come up with more things to try.