i have a video that plays on my iphone, but when downloaded to windows, only the audio plays and the video is black. help,

i have an iphone 4s. I can take a video and play it on the 4s just fine, i have always been able to down'load to my pc and view videos with no trouble. But since mid-october 2012, when i download the video to my pc, and try to play it, same as always, I am getting only audio and the video part is black. I can hear everything happening, but no picture. any thoughts?