A couple of options that may work:
• delete mplayerc.ini
Check rendering options like the following:
• mediaplayer->view->options->Playback->output->DirectShow Video->check VMR9 renderless
• mediaplayer->view->options->Playback->output->DirectShow Video->System Default
--- Click OK to save settings, close Media player, reopen, and try again.
• Try a newer version (With more built-in codecs, as based on FFmpeg):
http://mpc-hc.sourceforge.net/download-media-player-classic-hc.html That has a newish build (The original "Media Player Classic" is fairly old, and also apparently has some... potential issues. Media Player Classic Homecinema is updated to clear those issues, as well as adding in other options).
If you want something that's even MORE current, you can check here:
http://www.xvidvideo.ru/content/category/1/1/2/