Trouble with Halo, Combat Evolved

Just the other day I purchased the game and now I'm having some DirectX problems. When I tried to start the game, it closes and a pop-up appears saying that I need DirextX 9.0b or higher to run the program. So I get DirectX 9.0c, and unsurprisingly, it still won't work. I clicked run... from my start menu and searched for dxdiag, and it states that I have DirectX version 8.1. OK, so maybe I accidently downloaded that before the 9.0c, but still.... I tried to browse for 8.1, found something that appeared to be unrelated, deleted it, and it got me no where. Perhaps Windows XP is affecting the extract of DirectX 9.0b from HALO? I'm so lost and confused.

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My first question would be, is how did you uninstall the older version of direct x.

Did you just install new version on top of it?

Did you just remove files?

I'm think that there still may be something in the registry that says you still have the older version.

Nah, you're supposed to install over the old files.

Tell us your system specs. Your vid card may not even support 9.0.

I think you're right, the problem probably lies within the fact that I didn't even know what a vid card is until 5 minutes ago.... Truth be told, this is the first time I ever bought a PC game, so I know nothing about PC gaming. Doesn't windows XP have one already built in, or do I need to buy one seperately? How do I find out if there already is one? I clicked start, run, typed dxdiag, clicked display and now I don't know what to look for. If it's VDD, then it says nothing.

I wonder if there are any other system requirments I'm missing, I'll try to find out.