I found the temporary solution: restoring the pre-anniversary version.
Now I can play videos again. :p

Thanks for your suggestion. Yet it didn't work, even though I followed the instructions for 10 users (http://shark007.net/forum/Thread-Setup-and-usage), i.e. disabling media foundations and Microsoft...

Since the Anniversary update, I cannot play MKVs, MP4s and AVIs. I even installed the latest K-lite & CCCP after this. When I use WMP to play an MP4 for example, the program crashes. VLC plays AVI...