In order to fix this issue, try to restart Apple Mobile Device Service. Go to Start, type Services and open the utility. Select Apple Mobile Device and click Stop the service button from the left. After the service has stopped, click Start the service.
If this doesn't work, go to Control Panel and uninstall iTunes, Apple Software Update, Apple Mobile Device Support, Bonjour and Apple Application Support in this order. After that, go to (C:) > Program Files and delete all iTunes related folders. After the process is finished, download and install the latest version of the application from the official web page and restart your computer.