This is not the "screen lock" which asks for a passcode. Rather, it is like the "hold" switch lock. A tiny padlock appears in the upper-left hand corner of the screen and the wheel (menu, center butto, etc.) are totally non-responsive. The hold switch is NOT on, however, and I have toggled it several times to no effect. It stays locked.
I tried to reset, but the menu and center buttons don't respond.
I used "restore" on iTunes--twice--but that didn't work, either.
The iPod still syncs to iTunes and shows up on my computer when it is plugged in, but I can't get it to respond to pressing of any of the inputs.