Mine has just started doing something very similar. I have all the sounds set to on, they all work through headphones but not through the speaker. When I use the volume buttons without headphones it says 'sound effects' above the little speaker picture and the 'soundwaves' on the icon go from dull to white but I get no volume bars showing at the bottom. App volume is fine with headphones but none through the speaker, however the ringer volume and tones in 'settings' work fine through the speaker so I know that the speaker isn't blown. Any ideas anyone?