if you turn off/uninstall every codec, how is WMM going to decode your footage?
ffdshow can cause problems with WMM, so it's a good idea to go to your CCCP folder, click on FFDshow video decoder configuration and disable every codec that you have.
for example, if you have huffyuv, lagarith, divx and xvid you'd want to disable those codecs in FFDshow video decoder configuration. This stops FFDshow from trying to play files encoded with those codecs.
it's also a good idea to do the same thing in the audio decoder configuration. (when 2 codecs (be it video, audio or both) try to decode the same thing...it doesn't work out so well)
another thing you should do is make sure that Haali media splitter isn't splitting avi files. You can check/disable that from the CCCP settings (in the CCCP folder), do not click the Haali media splitter one (you can't change the filetypes that it tries to split from there). it won't be on the first screen, so you'll have to click "next" once
make sure that you aren't trying to edit with divx or xvid encoded footage, look at the FAQ for more info