Ah, yes. I've had that problem.
I recommend trying new things just for the sake of trying new things--things that are slightly uncomfortable or scary to do are best. I also recommend trying to cultivate your inner fantasy life, and ... well, just pick small things you want to change about yourself, and start working on them. Keep records. Give yourself pats on the back when you improve slightly. So, the goal shouldn't be "lose 500 pounds," but maybe it's something like "get a better haircut" or "keep my room slightly tidier." Little pieces of progress, the smallest increment that seems feasible. And focus on that, and keep going. Seriously, it works. Just go for it.
And, specifically, for the talking to girls problem: first throw the girlfriend idea out of your head and learn to be friends with girls like you're friends with guys. You know: "Hey, Roberta, what's up? What'd you do this weekend?" Not necessarily "hey bro," but if you need to start that way, then start that way. Then watch what other guys do, and figure out what you like, what you don't like, how you want to talk to women. But seriously--friends first. Forget the friendzone bull, having friends of various genders pays dividends you wouldn't believe.
You sound awesome, bro. I can't sing or play guitar, and I dearly wish I could. So just keep going. You've got what it takes.