Since I see that the OP has popped back in here, I will post as well.
It sounds like the very common mistakes that many parents make. In a way, I agree a little bit with the poster who said that yelling and giving in might be a big part of whether the child listens. I think there comes a stage in many children where we want to get their hearing checked because they have become Mother-Deaf!!!
I believe that listening, or NOT listening, is a learned behavior. Many of us might need to develop our listening skills!!
Maybe you could try this: When you say something directly to the child and you do not get a response, First, take a deep breath, don't take it personally and become frustrated. Go directly to the child, and make sure that they can hear you, and can make eye contact if they actually looked up, and repeat exactly what you just said in a nice even tone. (This might be considered the 'warning')
If the child fails to respond appropriately, then DO NOT repeat what you have said again. At his point, it would simply become yelling and negotiating and a battle of wills. Say to the child.. in a very authoritative tone, "Suzy(or whatever name), what did I just say to you, or tell you to do???
At this point, if there is not instant and immediate compliance, then immediately take firm but calm disciplinary actions. For example, take away whatever 'currency' such as TV, Game, etc. that may be causing a distraction. NOT ONE MORE word should be said. Instant consequences. (whatever the consequences may be.) No yelling, no bargaining, no begging, no threatening. Consistancy is very important, so it might be a good idea to give it some thought, and come up with some appropriate consequenses that will be used. It might be a good idea to have a nice calm discussion with the child to let them know just what the deal will be. This conversation should NOT be during or immediately after the latest yelling match!
It should not be long before the child learns to take you seriously.
Like I said, good listening skills are not a 'given'. I think they are learned. And good communication skills as well. I HATE people who always just walk by throwing out comments, or call out from the next room, or whatever, and simply EXPECT others who they feel are in any realm of earshot to be hanging on their every word. This is a HUGE bad habit.... So, always remember, when you are talking/yelling at your kid, your communication and attitude are laying the tone and the groundwork.