The same thing happened to me except I uninstalled steam because it sucked before. When I put it back, I wasn't even thinking, and I tried to make a new account when I reinstalled it. It wouldn't work. Eventually I managed to guess my original steam login and was able to get on through that.
However, you've been told several times to just try logging in to your original account. You haven't responded to that suggestion yet. The reason, I'm guessing, is because you don't HAVE an original account, you have a bootleg-assed piece of crap kazaa grabass version of Half Life that you took from one of your friends or some such crapola.
This forum has rules against trading CD keys and piracy. And whether your impossible reason ("my dad screwed it up"...you should get with the times, you're supposed to say it was your little brother, heheh) is true or not is irrelevant cause they don't allow that sort of thing here either way, legit or otherwise.
Why don't you just go buy the game again (assuming you bought it once)?