If you want to know which codec was used to encode certain file then get GSpot
http://www.headbands.com/gspot/
(beta works ok, so you can get 2.52)
Then you open file in GSpot, and check video codec section.
When you know what codec was used, go to ffdshow preferences, and try to change something there.
If you still see no picture, then probably the only way is to disable ffdshow handling of this codec and install original one.