On my computer, there are four places to check sound level.
First, in game: Do you have your sounds all the way up for both the music and the effects?
2nd, OS control. Do you have the sound on your computer turned on?
3rd Keyboard volume controls. Have you used your keyboard volume controls to turn down the OS volume?
4th Speakers. My little external speakers have a volume control as well.
You might see if one of those settings is turned down.