While trying to test an Android App on my Goolge Nexus 4 (LG edition) by selecting “Run as -> Android Application” inside Eclipse, the device manager did not offer to select my nexus.
Opening a command line (Windows 7) and running “adb devices” also returned nothing.
However, my Nexus was successfully connected to my computer and I was able to access the device storage from the Windows Explorer.
Finally, the solution was to switch my Nexus USB Storage Decice mode from MTP to PTP. This can be done in the storage managemed (under Settings -> Storage -> USB Computer Connection.) The disadvantage is, that opening your Windows Explorer, you get only access to what the camera mode of your Android device provides you. However, now you can run and test your app and even copying data to your device is not an issue. You can simply switch back to MTP mode whenever you want to.
Related discussion on StackOverflow: http://stackoverflow.com/questions/14005176/adb-not-recognising-nexus-4-under-windows-7