Here is my answer as previously at Why cant I do a hard reset to the screen to unlock
"If you forgot the combination, the only way to unlock the iPod and enter a new one is to reset it to factory settings. This means that you will lose all your data on the iPod. To restore the iPod to factory settings you have to connect the iPod to its primary computer and select “Restore” from iTunes > Summary tab.
THIS WILL MAINTAIN YOUR DATA
Now I think if you are using windows you can also try to
1.Plug the iPod in computer.
2.Go to "My Computer" And click the apporiate drive your your iPod.
3.Change folder option to "View all hidden files and folders"
4.Go to ipod_control
5.Then to Device
6.You should see a file there named "_locked"
7.Open that up with a text editor (Notepad) and the passcode should be right in there.
or of course you could just rename the file to _unlocked
Close your text editor and eject iPod from computer