Download and install it again.
http://www.microsoft.com/windows/directx/default.aspx?url=/windows/directx/downloads/default.htm
I tried to run dxdiag and I get this error: "This is the Unicode version of dxdiag which only runs on windows NT. Please use the non-unicode version for windows 95 and windows 98".
How can I fix this problem? The computer shows that I have dxdiag 5.1 W/NT. HELP! Thanks!

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