I have read your entire posting, interesting read my friend.
First off, let me tell you depression is common amongst teenagers, how we handle the situations are much differently depending on who we are as individuals.
It seems you are addicted to the computer (obviously) when school should be a first priority, I had the same problem when I was your age, however I was somehow able to maintain good grades. There is no magical cure for this, the only logical explanation is self-control, you need to control your urges and limit your computer usage, sit down and do your homework. Since I was in your situation, I know it is much more difficult then it sounds for someone who isn't use to it, but
YOU need to
WANT to change before doing so.
However, I always was well-known in my school rather than being socially isolated, however you seem to be extremely pessimistic towards yourself, you need to be a little more confident. Being a virgin isn't necessarily bad, you need to realize there are over 6 BILLION people on this planet, finding that special someone takes a little longer for some than others to locate.
Summer school, as much as it sucks, might help you and your addiction to the computer and going on lawn mower forums (lol), you need to fight this addiction.
Hanging yourself doesn't solve anything my brother, nothing at all. Do you happen to cut yourself if I may ask?
Why did your relationship end by the way?
As for sex advice, give me a PM sometime, I can give you some tips and hints, promise.
You need to identify what causes these suicidal urges, when you feel the need to hurt yourself, you then need to tell someone so they can prevent you from actually doing it, this person needs to be someone you sincerely trust, even if it is an internet buddy, it is much better than nobody at all, but preferably have it be a RL buddy.
What are you looking to solve in this thread? Your thread is very broad, what specifically are you wishing for?