what codec packs do you have installed? if you ahve several installed uninstall then and only install those you need. you can also check what codecs are needed by using G-Spot
http://www.headbands.com/gspot/download.html
what does Bsplayer show when ur playing teh video? you can check that by right clicking bsplayer>options>filters it should tell you there what codecs are used and stuff.