Perhaps this can help, if you have installed the graphic-software "IrfanView":
Some weeks ago in Studio One I could import my video and I could extract the audio but I couldn't see/play the video.
After checking bitrate etc and re-installed video-codecs the problem resists.
Then I checked IrfanView, going to "options" - "settings" - "video/music". There was an entry "internal video-player" checked. I changed it to "use external video player".
And now, in Studio One I can play and see the imported video and could go on with scoring the filmmusic to my video.