It definitely sounds like you have taken some great troubleshooting and isolation steps. Let's see if the following information resolves this issue:
- From the Start menu, choose Control Panel.
- Select Network and Internet and select Internet Options. Or in Classic View, open the Internet Options control panel.
- Click the Connections tab.
- Click the LAN Settings button.
- Select the "Automatically detect settings" checkbox.
- Click OK in both windows.
- Reopen iTunes and connect your iPhone, iPad, or iPod.
- Update or restore your device.
If the above does not resolve the issue, please see the "Additional Information" section regarding the hosts file.
Usually, there is one and only one reason for that - something blocks that connection. Windows firewall to my small experience is not strong enough to to that. So you need to check two things as far as I am concerned.
1. you need to check your hosts file. If you know how it suppose to look you ll see difference right away. If you don't just use "Microsoft fixit" for host file program (Google search)
2. If disabling antivirus does not help -uninstall completely - I do not want you to not have antivirus, just eliminate as a threat. Sometimes the problem is not current antivirus, but the remnants of the previous, run clean up tool for previous. (Google "Norton clean up tool" or mcafee ....)
If this two things do not help you - at the very least try to create another user account and see if the problem exists there.