My Samsung phone was not recognized by Android Studio on windows 7. I repaired it by installing the Samung Driver here: http://developer.samsung.com/technical-doc/view.do?v=T00
I solved in following way:
Go to Settings->Developer options-> On top of the screen, turn on the button.
Now goto bottom on the debugging section.
Now turn on USB debugging option
It will ask some questions if you want to allow the PC to this device, press allow all time!