It a drastic measure but if you want to start from a "clean" install (I presume you have your data backed up) in order:
1) Clean install of Windows (preferably Win7) and run the Windows update over and over till it is all up to date
2) Install latest version of your Video Card drivers (what Video Card to you have? what connection output are you using to your TV/Monitor? eg HDMI, DVI, VGA, Component, S-Video, Composite)
3) Install latest version of your Audio Card drivers (what Audio Card to you have? what connection output are you using to your Receiver? eg HDMI, Analog, S/PDIF)
4) Install latest version of MC and restore you library & files (you should now be able to play Audio files just fine as you don't need filters to do this)
5) Install CCCP (you should now be able to play almost all Video files)
6) Take a snapshot of this working system so you have a "last good" backup you can restore from
7) Tweak your settings, add specific filters, other application (TV tuners etc etc). Each time you are happy with the results then update you "last good" backup.
Your setup is probably not that bad it requires a clean install but it is very hard to work it out what to fix without being there, so another option is that some kind MC'er may live around the corner and for a few beers may be able to have a look see.