Don't know if this has been solved yet, but I was having the same problem, and this worked for me: http://www.technipages.com/itunes-fix-iphone-or-ipod-not-detected-in-windows
If you can't/don't want to use the link, I'll write it out here:
1: Ensure the latest iTunes is installed
2: Open "Control Panel"
3: Select "Hardware and Sound"
4: Select "Drivers and Printers"
5: Your iPhone or iPod should be displayed in the "Unspecified" section. Right-click it and select "Properties".
Note: If you don't see your device listed here, ensure you have selected to trust the PC on the device and you are using a supported cable.
6: Select the "Hardware" tab, then click the "Properties" button.
7: From the "General" tab, select the "Change Settings" button.
8: Select the "Driver" tab, then select "Update Driver"
9: Choose "Browse my computer for driver software"
10: Select "Browse..." then navigate to "C:\Program Files\Common Files\Apple\Mobile Device Support\Drivers" If you don't have this folder, check in "C:\Program Files (86)\Common Files\Apple\Mobile Device Support\Drivers".
11: Click "Next">"Close"