try uninstalling itunes, also, find the ipod in device manager and uninstall it there.
then, reinstalled itunes and plug the device after installation is completed
before you do that you might want to try close any software that uses your USB port - your printer software for example. Often with USB devices their associated software will sit there waiting for a device to be connected and it can prevent other devices working.
For example my printer wont work if MS activesync is active waiting for a USB connection.
If you cant close the software go to start and run and type msconfig. Then click on the startup tab and go down through the list of items and disable anything that might be loading on startup which uses the USB port. Click apply and restart your computer and try your ipod then.
go to control panel
Select System
Go to the hardware tab
select device manager
Plug in your ipod and see if any new hardware appears
If you see it appear right click on it and select uninstall
When it vanishes go to the options up the top and select search for new hardware and it will auto detect again and hopefully will install correctly this time.