Aren’t the codecs you installed enough yet? Windows Essentials Codec Pack is a complete package for your Media Player Classic player with which you can open 99% -according to its creator- of all video and audio files.
In addition, Windows Essentials Codec Pack has the advantage of being continually updated, so that you'll be in touch with the latest codec issues and updates.
Windows Essentials Codec Pack supports the following formats: 3GP, AAC, AC3, APE, AVI, DivX, 3ivx, DAT, h.264, x264, AVC, Nero Digital, DTS, FLV, FLAC, HD-MOV, MPEG-1, MPEG-2, M4A, MPC, MP3, MP4, MO3, MOD, MKV/MKA, MTM, OFR, TTA, OGG/OGM, S3M, Vorbis, VOB, WavPack, ATRAC3, XviD, XM, WV, UMX.
The only disadvantage is that it does not have the necessary codecs to visualise QuickTime y Real player formats; otherwise the package is perfect; don’t forget it: Windows Essentials Codec Pack.