Q:

My Emulator is Not running. Even nothing is showing in the Logcat. It shows "No Connected device" and "No Debuggable pro"

I have not connected any physical devices with the system.  When I am selecting any virtual device, it not takes. 
Logcat shows "No Connected Device" and "No Debbugable process". I tried to end the adb.exe through Task Manager, but it starts again and again.
Earlier it was working fine. But don't know what happens it right now. I searched lot but not able to solve this. 
6:00 PM * daemon started successfully
6:00 PM Executing tasks: [:app:assembleDebug]
6:00 PM Emulator: emulator: ERROR: Another emulator instance is 
    running. Please close it or run all emulators with -read-only flag.
6:00 PM Emulator: Process finished with exit code 1
6:00 PM Gradle build finished in 1 s 783 ms

I am new in Android so please tell me step by step

A:

Looks like you might not be listening to the error being thrown by the emulator but in any case, go to the folder where the AVD image is stored. 
On windows, its C:\Users\<user>\.android\avd\AVDname.avd and delete any .lock file in this folder. the emulator should restart properly. 

