Why do my headphones only pick up louder sounds?

For example, when in videos on youtube, such as background music, it sometimes doesn't play any sound until a dominant sound like talking comes on. Same with games. I was playing Gmod and Minecraft, and it can't hear the footsteps, or the swinging of a weapon. I've been having this problem ever sense I moved to my desktop from my laptop. I'm using CoD: Ghost Turtle Beach headset. I've made sure that this is the default speaker as well. I have my computer on the floor, so I can't use just the cord coming from it to connect it to my computer. I have to use the extended cord that you'd use for a console and stuff that has the sound box on it where you can increase the sound and voice and mute the mic ect. I've tried playing around with that, and it doesn't seem to fix the problem. I also had some speakers set up for my computer, but I removed them, thinking that it may be the cause of the problem… It wasn't. My headphones are plugged into the front of my computer but 2 chords. Once of them plugs into the headphone jack, and the other is a usb cord thing. I don't think they will work without either one.