After googling for days and trying 1001 solutions, I decided to post here for further advice. I have a Nexus 4 phone, Windows 7 x64 Ent with latest updates, google USB Driver installed.
My phone appears in device manager as an Android Device, but not under Portable Devices, and nothing in My Computer in windows explorer.
I have tried in my laptop with the same windows etc, and it works fine there; in that case, the "Android Device" entry is missing, but the phone appears instead under Portable Devices and I can access it through windows explorer as if it was another drive.
With the above said, I discard any issues with either the cable or the phone setup.
Update: trying the following guide http://www.londatiga.net/it/how-to-use-android-adb-command-line-tool/
when i type "adb devices" it doesn't find the Nexus: