Problem setting up an Android device for Build & Run?

While my apk is built fine using only the build option, I cannot get the Build & Run option to work.
My device is a nexus 7 - which has it's drivers installed correctly I assume (It works with Unity remote 4).

When trying to use Build & Run - The process get stuck on "Trying locate a suitable Android device..."
followed by another popup saying: "Build failure Unable to retrieve device properties. Please make sure the Android SDK is installed and is properly configured in the Editor. See the Console for more details."

The error reported in the console:
"Error building Player: CommandInvokationFailure: Unable to retrieve device properties. Please make sure the Android SDK is installed and is properly configured in the Editor. See the Console for more details.
C:/Program Files (x86)/Android/android-sdk\platform-tools\adb.exe -s 015d483b8523fa0b shell getprop"
stderr[
error: device offline
error: device offline

I then run "adb devices" in cmd window - I get a single item in the list of attached devices with a status saying it's offline.

So in both cases it says my device is offline...How do I correct this?

Edit: for some unknown reason the device changed it status from offline to device...- No idea why this happened. But problem seems to be solved regarding uploading the apk to the device.