Sound problems on macbook pro!?

I have a macbook pro and it has started having problems with the sound! The problem is that even if i press the raise/lower sound buttons, the sound stays exactly the same. It gets temporarily fixed if I restart the computer or reset PRAM, but soon the problem starts again. Sometimes the sound is fine until I take out the headphones and then the problem starts again. I took it into the apple store and they looked at it, but the problem came back when I got home. Also the volume icon at the top never changes anymore, even if I lower or raise the volume. I have no idea what is going on but its becoming increasingly frustrating to restart the computer if I want to watch a video. I have not been running any new programs or anything that would affect the sound. Does anybody know what is happening? If you could help I would be forever grateful!!!!