Evidence shows using a computer changes your brainwaves into a pattern that is not great for sleep. It doesn't mean you can't use a computer than go to bed, it just does not help.
If you REALLY want to go to sleep, get off the computer about 15 minutes to an hour before sleep. Go to bed at 11PM. Eating things like cherries half an hour before sleep helps you, because of the natural melatonin content.
Staying on your computer till late won't help you sleep. Even if you aren't tired, going to bed will help dramatically when you are in the dark and laying down; your brain recognizing you are in position for sleep will help alone.
Also, if you have a lot on your mind get up and think it over before going to bed. If you have thoughts while in bed, don't focus on them; let things pass through your mind. Focus on breathing if you want to keep your mind off things. Keeping still can help you become tired (but don't get caught up in not moving, that'll make it worse).
Don't do other things in bed like sit on a computer or other crap; reserve the bed for sleep (and love but most people here are probably too young / too nerdy for it haha). The mental impact of that will help, as again, your brain with associate beds with sleep and sleep alone.
EDIT: Oh also, you need 8 hours recommended for healthy sleep. If you wake up a lot, you aren't getting to a deep stage of sleep necessary for a good nights rest.
