roller coaster tycoon problem..please help!

hey um roller coaster tycoon cant be played on my computer, after i downloaded the game i went to play it and it says direct x 9.0 cannot be found, but i have downloaded direct x successfully a whole bunch of times! and it still says that it cant be found!!! can someone pleeease please help me ireally want to play my game! and i also tryed dowbloading the trile version but it does the same thing. i have all the system requirements.. well im almost positive i do,, we jsut got a new computer so i think everything should be up to date.. its one of those new dell ones that you see on all the dell commercials... PLEASE HELP!!