Rint,
You need self-esteem. You need motivation. You can get those by exercising. Want to fix your life? Stop feeling so damn bad about yourself and FIX things. Reading the DJ Bible will not take that long, so just get it done. The one thing you need to realize is that you may not want to do it, but if you start on it you will slowly begin to have the urge to -finish- it.
This is how life goes, so start on one thing, then when you finish it start on the next solution. Once you finish the DJ bible, try getting out of the house more often. To bring your grades up, go read your textbooks outside everyday. Getting some sun helps you in many ways. Turn off your computer until X pm everyday, put restrictions on the things in your life that distract you from living -life-.
Once you get your mind on the right track, everything will fall into place and you will be a better person.
Keep your head up, build up your confidence, cut out the wasteful things in your life (tv & computer), and start living life my man! Remember you only live once (or so I have been told =D )!