My Recommended Codecs

I spent some time trying to get my computer back working after the AVG fiasco and I could not get WMP to play all my video files like it did before. I ended up trying k-lite pack, cccp, divx, xvid, ffdshow,matroska pack lite, vsfliter, matroskasplitter, and ac3filter

All the the packs caused little secondary issues and some would play video but no audio and vice-versa.

My final pick was installing only  VSfilter, MatroskaSplitter and AC3Filter
http://haali.su/mkv/ MatroskaSplitter
http://ac3filter.net/wiki/Download_AC3Filter AC3Filter
http://www.videohelp.com/tools/VSFilter-DirectVobSub VSFilter

I installed AC3 last. When I installed vsfilter last I could not fastforward or skip to a location in the movie by dragging the progress bar in WMP.

This is not what I had before the last format but so far it is working on everything and has additional functionality. They add icons to the taskbar that are useful.

Haali (aka MotroskaSplitter) gives you the option to select from multiple audio tracks. Something that WMP12 lacks as far as I know.

AC3Filter gives you these options

Finally VSFilter for the subtitles 

Good luck. A codec pack might work for you but I did not have any luck with them.