Try this, it worked for me after nothing else here would:
Open the windows firewall settings, and look if "SyncServer.exe" is allowed. I'm gonna guess it isn't even listed 😝
Instructions (Windows 7 x64 - Vista is probably similar):
Open "Control Panel"
Select "Windows Firewall"
Click "Allow a program or feature through Windows Firewall"
Look for "SyncServer" in the list. It won't be there.
Click "Change Settings" then "Allow another program"
Click "Browse..."
Find "C:\Program Files (x86)\Common Files\Apple\Mobile Device Support\SyncServer.exe"
Restart iTunes and your iPod/Phone/Pad should appear in iTunes even when disconnected. If not, try rebooting to make sure everything is reloaded properly.