I am totally addicted to my computer -.-
Basically I'd say set a timer. Only allow yourself to go on your computer for 2 hours a day, or 4 hours a day. When you have been on for that time, get off the computer. Go for a run/walk, play a game, sing a song, even just go to bed! It can be really hard, I know. But getting out and having fun away from the computer is important. =]
I hope things work out for you