I understand you pain, too. I can stay on my computer for so long that hours will pass and I won't even realize it. You really have to dicipline yourself. That is what any kind of "drug" is about. When you let it take over your life and it starts to take over your decisions, that is when you are addicted. But the good thing here is that you know you have the problem! You just have to dicipline yourself. Do you homework first! Only let yourself stay on the computer for a set amount of hours a day.
If it makes you feel any better, check this out.. When my boyfriend wakes up, he goes straight to the computer, plays around for about 45 minutes. Goes to work at his computer job. Stays on the computer ALL DAY! Comes home, eats dinner, gets on his computer until he goes to sleep. Some nights he will read or watch a movie. But there will be computer in-between. He doesn't reconize this as a problem, and it isn't. It doesn't influence him to slack off in different areas in his life. You know, he still goes to work, and all that fun stuff. It is a problem for you because you are almost depressed about it. Just dicipline yourself. That is what makes people in control of their life! Practice it, and make sure the things you do on your computer a benifical to your well being. These health forums are good, researching, studing, learning, even games are good for hand/eye coordination (just not too much of them).
ps. sorry for any spelling errors!