Please help (DirectX issue)

Ok so ive been using my comp for some time now with no problems but today i got the game Republic commando. I installed it and tried to play and it says something like "you need directx 9.0c to play" so i press install directx, it goes through the whole install thing in like 0.0001 secs and says complete but when i press play it just repeats "need directx 9.0c" .

I go and check in Dxdiag to see which version ive got and it says "directX : Not found" ??? Ive tried downloading from different places and getting both netinstall and the "non-internet" install versions but doesnt help.

Also in some updates it gets an error telling me to check error file and this is what the error file says: 

03/07/06 17:17:00] module: dxupdate(Sep 28 2005), file: dxupdate.cpp, line: 178, function: GetDXVersion

    Failed API:        RegQueryValueEx()
    Error:        (2) - Määritettyä tiedostoa ei löydy.



    Current DirectX may be a older version which does not have the version value in the registry.

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[03/07/06 17:17:00] module: dxupdate(Sep 28 2005), file: dxupdate.cpp, line: 3937, function: DirectXUpdateGetSetupInformation

    GetDXVersion() failed.

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[03/07/06 17:17:00] module: dsetup32(Sep 28 2005), file: dxupdate.cpp, line: 244, function: CSetup::InstallPlugIn

    DirectXUpdateInstallPlugIn() failed.