when i download a video clip to from computer to my phone it says canot run or start.
YouTube videos are usually either FLV or MP4. If it was in MP4 format, your phone should be able to play it. So if it was FLV, you can still watch the video on your phone. All you have to do is download a video player app. I would suggest you try MX Player Pro. That's the app I use as an alternative to the native video player on my devices.