I have the same problem, and it was once just as bad as what you described. It's less of a problem now and it's not keeping me back socially anymore, but I should spend more time on my study. So I'm still struggling with it, but I'm on the right way.

Some general advice: start cutting down your PC time slowly, but steadily. You shouldn't aim for abandoning it entirely, just reducing it to a point where you can be happy with it. Find other activities for your free time, even sitting down and reading a good book is an improvement. Also:

Quote Originally Posted by Garcilaso de la Vega el Inca
One or two weeks ago, I had an important talking with some classroom mates, and they told me to have a better social life.
If these classmates are friends of yours or if you think they could be good friends (be careful though if you don't know them well), you should see if you can hang out with them outside schooltime.
I personally never made any lasting friendships during "high school" but I looked elsewhere and ended up finding plenty. Join a club of some sort, music/sports/whatever.