It should unlock after connecting it to the PC it was registered/first opened with. If not, then you can backup your songs/videos to your PC, then restore your ipod, then transfer the songs to your iPod again with Itunes.
To back it up:
Go to My Computer. Open your iPod. Go to tools -> Folder Options -> View -> click on "Show hidden files and folders", then click OK.
Then go to iPod_Control, then Music. You should now see a bunch of folders starting with F, for example, F00, F01, F02...
Open up each folder, then copy the contents of each folder into ONE folder ON your PC. Don't worry about the names of the songs, I'll get to that later.
To restore it:
Open Itunes. Under devices, click on your iPod. Then under the summary tab, click restore.
After it is finished restoring. It's time to add the songs/videos again to your ipod.
To add the songs/video back to your ipod:
In itunes, go to File, click on "add folder to library", and open up the folder where you saved your songs/videos. They should now be in the itunes library. Then just simply drag the songs from the library to your ipod, and wait for it to finish syncing.
If the not all of the songs open up, then you may need to add a few at a time (this happens with some computers). Go to file, add file to library, locate your folder with the songs, and select a few items, then repeat till all of them are loaded in itunes.
