can't play

[G-Dub]

i've mailed gabe about this but haven't got a reply yet.

in short... i installed hl2 from dvd, activated it etc... watched intro etc and had to go out. shut down computer normal way and basically whenever i try to play now it says i need to put in the dvd... but the dvd is in the drive.

i'm sure i've tried everything possible! is there a nocd thing out yet? it's so annoying, i have the game and can't play!!!