Half-Life 2 no steam patch?

I bought Half-Life 1 & 2 in a pack online and download 1 and played it all the way trough with no problems with activation codes or anything. Then i tried to download half-life 2 and download the 6 discs then it asked me to put i activation key. I tried the one it had and it said "already used. please try again"... so i kept trying and it never worked. now im wondering if i can play it without steam. Like maybe a patch? thank you for your help :D