See Here > http://support.apple.com/kb/HT1808
You may need to try this More than Once... Be sure to Follow ALL the Steps...
Take your time... Pay particular attention to Steps 3 and 4.
Some users have reported as many as 8 or 9 attempts were necessary before success.
- I would start with
However, after your remove the Apple software components also remove the iCloud Control Panel via Windows Programs and Features app in the Window Control Panel. Then reinstall all the Apple software components
- New cable and different USB port
- Run this and see if the results help with determine the cause
- Try on another computer to help determine if computer or iPod problem