How do I fix my social skills?

Brief info about myself: 18 years old, first year university, good grades, horrible social life, extroverted once i start talking to someone, but I find it completely impossible to go up to someone and start a conversation.

Brief summary of the evening:

Normally I don't leave my house except for school and work, but I've been working on my social life and trying to change that. However, it's been difficult. I saw a page on facebook for a frathouse kegger, and I texted a friend and asked if he wanted to go. He said sure. Now normally I wouldn't go to something like that, but because I was going with a friend I figured it would be alright.

So we go there, and there's something like 200 people crammed into this frathouse, and everyone is essentially in their own groups having a good time. I was intimidated to say the least, but I decided to start the drinks flowing to get a buzz going and see if it would help my shyness. I was semi-drunk, and there were tons of people everywhere, but I still couldn't bring myself to go up to anyone and just talk. I have no problem talking to people even if I just barely know them, but I can't go up to someone out of the blue and start a conversation. I just feel so self conscious in situations like that.

I talked to a couple people (they initiated it) while we were in line for the washroom, but then right after I finished it was right back to the wall to stand with my friend.

I know I'm gonna get a million responses saying "Oh, just go up to people and say hi", but the whole point of this thread is that I find it very hard to do that. It seems like most other people were in groups of their own friends talking and having a good time, and I find it very hard to go up to a group like that and say anything.

I would appreciate any advice you guys have for me, because I want to make the most out of my university career. As much as my actions may seem to the contrary, I don't want to be a wallflower for the rest of my life.

Many thanks in advance.

Duly noted, and the first paragraph makes a lot of sense. I guess I shouldn't be expecting to have great conversation at a kegger. But I guess the main point is that I need to address my issues with starting conversations. When I don't know the people at all, I feel like the odd one out, and very self conscious. However, if anyone comes up to me and starts talking, I don't have a problem carrying on a conversation. I just don't get it.

And w.r.t the clubs/extracurricular aspect, I really haven't done anything yet, because, like I said, I feel very awkward around people I don't know. However, I am really trying to break out of my shell, and I'm gonna do my best to join some things at the beginning of the next school year.

Thanks for the advice. For me, simply going to this was "throwing myself to the wolves". Normally it would be another evening of sitting alone at home wondering why I can't make friends. But I completely understand what you're saying.

Thanks for the good advice guys. Yea, I'm not trying to just go throw myself on anyone, anywhere and start talking. I just want to be able to go up to someone (say in one of my classes or whatever), introduce myself, and be able to talk to them. But for some reason I find that near impossible in pretty much any situation. The talking part after I've been introduced is fine, but I can't bring myself to just walk up to someone and introduce myself. As I said though, I've been working on it lately, and hopefully it will just "click" sometime in the near future.