Reinstall HL2 direct-x prob

[big_king_frosty]

My "friend" had leant his copy of HL2 to another friend. He claims that he uninstalled the game but when he did ther were "small" files left on the comp, although when he turned steam on it still had "play HL2" on it. Now that hes got it back hes trying to install it and when it comes to the installation of Direct-X it shows the "better version installed" then when he clicks next it goes on to a blank screen doesnt load and does nothing!! anyone had similar probs, greatly appreciated!!