Hello koushik Biswas,
Make sure you have the most updated version of Realtek HD Audio Manager.
Go into your Realtek manager. Click on "Device Advanced Settings" (Top right corner). Select "Make front and rear output devices playback ... ".
Then click on the little folder under "Device Advanced Settings" and select "Disable front panel detection"
You should now have what you see in the following picture. Right click on Speakers (circled) and select "Set Default Device" Also make sure that your microphone is your default device and that the volume is turned up.