Window movie maker,problem

i just created a video on window movie maker,the essential one on window 7.after I saved the video ,i play it on window media player,and what I see is the screen is black but audio is played.Omg please help me im dying here,i am using mp4 format for that video.Please answer this ASAP please?

i am sure before saving as movie you save it as project if you do like this so need to eorry save as movie again otherwise you are doomed