Help Needed For DirectX Problems

I'm having problems with DirectX. I'm running a fully up-to-date Windows XP. I'm not sure what version of DirectX is installed, but all the files in the DirectX Diagnostic Tool list are from 1998 at the latest.

I've tried using Windows Update to get the latest version, but it doesn't recognise that the version I have is so old. I tried downloading DirectX 9.0c from Microsoft, but when the installation wizard runs, it appears to work, but then finishes immediately without having installed any files. I tried loading 8.0 and 9.0b from various game CDs, but the same thing happens - finishes without actually doing anything.

Any game I try gets so far into loading, then tells me that I need a higher version of DirectX to play and quits.

Any help would be greatly appreciated, as the Microsoft DirectX Troubleshooter led me to an answer of "No idea. Try somewhere else for help", or words to that effect.

Thanks.