iphone 4S not playing voice memo
Your voice memo is being played through the earpiece speaker. You can listen to it, just tap play and put your iPhone up to your ear, as if you were taking a phone call. 

To play through the loud speaker, like almost everything else, tap the speaker icon in the top right, it should turn blue. Now play your voice memo like you normally would and it will play through the loud speaker, as opposed to the earpiece speaker. If it doesn't, ensure that the silence switch on the left side of your iPhone is up and that the volume is on.