Q: unlocking my 3rd gen nano

I'm the second owner of a 3rd gen nano (no disk or manual).After using it several times on my pc with Vista Home premium and on one with windows 7, I started getting a can't recognize a usb device error when i plugged it in (only shows up in control panel as an unknown device).  I've tried several usb ports (all 2.0) and several cables- same result.  I've updated Os and iTunes, gone through the 5 Rs and tried all suggestions on the Apple support page - no difference. the latest wrench is that my granddaughter accidently locked the screen and I don't know the unlock code.Since I can't get the computer to recognize it, iTunes doesn't "see" an ipod so i can't sync or restore.  The battery is completely charged and if I dock it in my home theater dvd player it still plays my stored tunes.  How do I get it unlocked and how do I get my computer to recognize it?