VLC showing grey screen???

Hi, i know this type of question has been asked here before, but i cannot seem to find the thread for it. therefore, i have made this new thread in trying to help fix my problem.
when i try to play some video files in vlc the sound seems to work fine but the video is not displaying. instead it just shows a grey screen, or even a black screen for where the video should be displaying. can someone help me to fix this problem and be able to show the video being played. thanks for any help in advance.