No Sound when receiving at text in sleep mode

[sashapoo]

Hi everyone I'm hoping you can help. I got my HTC Imagio two weeks ago and at first it was working fine but for the past week to week and a half I get no sound notification when I get a text message and the screen is off. On occasion it will light up but no sound. So if I am not constantly checking or staring at my phone I have no idea if I get a message or not. I have checked the setting and the box is checked. I can hear the sound when I press play in the settings screen. I have also tried a soft reset and that didn't help any. If someone could please help me I would be greatly appreciative. Oh and if you could dumb it down a bit that would be helpful, Im not the most technically gifted. Thank!!!!!