There is few things you can try remove all the codec packs and Media Players like VLC, K-Lite, Shark007 and reboot the system. Then use the troubleshooting tips in the tutorial. You have to use the whole string not just msdt.exe it's msdt.exe -id WindowsMediaPlayerConfigurationDiagnostic
that will open without passkey. Once all of the sections are complete download VMCD
it will reset the Decoder to default settings. (Even if it's for Vista I would assume it should work for Windows 7 as well) but create a System Restore point before making any changes. Then reboot the system install Shark007 codec and try it again and see if it works.
Hope this helps!