No audio when playing back recorded vocal etc

hi using a Yamaha mgxu mixer it is correctly mapped and there is audio when recording and you can see the waves in the bar of recorded vocals etc on Cubase AI when I play back the audio (tried pressing the monitor button on /off ) there is no sound when I am singing through the mike you can see the information is going through as the volume input bar is going up and down and as I say the waves are been recorded on the recorded box.