Getting Error when trying to play video files

i have already tried posting this in another section of the forums and nobody has helped me over there so i will post this here when i try to click play all when playing video files i get the error saying no playable file is found, but i can open up a folder and play video files individually though i have tried everything from resetting Windows Media Player to disabling it and re-enabling it and i am not having any luck, i did look online and find out that i may have to go and edit the registry to get it working again and i have no clue on how to do this i am trying to play mp4 files and i am running Windows 7 Professional, if anybody has any solution for this please let me know thanks

i will try it when i get home later i am sending thia through my phone right now, thanks for the suggestions

this solution worked and now it is working again glad I got it all straightened out, I am kind of curious though on why it started doing that it was working fine earlier this week