Can't connect an already booted device to adb
I have had similar trouble with a different device.  After you plug you device in try:

adb devices


If your phone is not listed, try restarting ADB:

adb kill-server
adb start-server


Lastly, check if there are any driver updates for your phone.  A good place to start looking for drivers is Google's OEM page and Samsung's support page.  Additional tips might be found on this SO question.