audio ok, black screen

Hi, I´m a newbie in BSP. My problem is that i get the audio correctly, but I can´t manage to get the video. I´ve tried installing and uninstalling different codec and codec packs, including the codecs recommended in this forum but all I get is a black screen. Could someone help me?
If I go to preferences-video, I see as tthese options as if they were disabled : divx 3.11 preferences, divx 4+ preferences , and FFD show preferences.
Is there anything I do wrong?