osvaldo, have you tried this from here
1. Connect your iPod Touch to iTunes
2. Press or Hold the power and home keys 10 seconds.
3. Screen goes black, now release the power button
4. Make sure you do not release the Home key until your iTunes says "We have detected an iPod Touch in recovery mode."
5. Restore the iPod
and if you are using a PC, there is one more way if you do not want to lose your data First plug in the ipod, go to My Computer. Click on the ipod drive, then go to tools > folder options. Then click view, click show hidden files. Go to ipod_control. Then go to device there should be a file named "_locked" ,delete that. Unplug the ipod and you should be ready to go hope this makes sense,