Is there anyone from the old job that can give you a good reference? If so, I would not worry too much about the fact that you walked off the last job. Even if not, you can't let worries about quitting your last job affect you. People quit jobs all the time. Come up with a text-book response for when people ask why you left and just be done with that part of your life.

You mention wanting to start a company but not being good at networking. I HIGHLY recommend working on your networking/social skills. These skills are far more important when you are self-employed than when you are working for someone else.

I'm working on those kind of social issues you mentioned by signing up for a lot of interactive events, like Meetups, and signing up for potlucks and other stuff like that offered by some organizations I belong to. At first it was torture, but it is getting easier!