Were you moving through check or already moved your King or Rook prior to attempting to castle? I'm finding it odd that you say you've played 10,000 plus games but only recently began to take a learned interest in it. 10,000 games sounds like a very committed chess player.
See if you broke any of the conditions described here: http://en.wikipedia.org/wiki/Castling
In my younger days I used to play speed chess on yahoo just for fun during breaks and lunch at work. But I'm a little older and wiser so now I would really like to learn to be a more skilled player, not a haphazard one.
I wasn't clear i the first comment. I was able castle but the computer never did. It did not castle its own King. Perhaps to protect a pawn? I just found it odd.
Could be the difficulty setting, or it could be that the computer didn't want to castle because it had better moves to make. 
I castle many times my computer=Mack-Book pro is reliable in alowing the castle move
To "castle during first ten moves" is more of a simplistic advice for beginners than any objective truth about the game. Following it probably prevents a beginner from making some typical mistakes but it's not always the best way to play. An experienced player may sometimes castle much later or not at all because she is better able to judge when the time is right. More truthful but more difficult to apply rule might go along the lines: "castle when it's necessary to secure your king or advance your plans and there's nothing more usefull to do".
Also, imo it's a bad idea to try to copy the way the computers play. Even more so with these computers in live chess which are far from full strength and sometimes make strange choices because of that.
"Castle when you wish to, or when you must, but do not castle just because you can".
All three computers I have played against (easy, medium, hard) castle. I have seen a few games the impossible one played and it castled, too. Just go to their homepage and check recent games.
To "castle during first ten moves" is more of a simplistic advice for beginners than any objective truth about the game. Following it probably prevents a beginner from making some typical mistakes but it's not always the best way to play.
That makes sense. I've a lot to learn.
In some of my recent games I've castled much later. I've had a few games where I castled early and the opponent attacked my king quickly.
Hello, Even though I've played 10,000 plus games of chess it's only recently that I've begun to actually take a learning interest in it.
I've played the chess.com computer set to medium a few times. I noticed that in the first three games it never castled. I thought castling was something one should try to do within the first ten moves.
If that is the case, why is the computer not doing it? Am I mis-informed?