Why when I watching video on YouTube, video stop but audio continue. And when I move the mouse then video start playing again. Every time video stop I have to move the mouse... Please help me..

It sounds like you are having some problems with codecs and or flash player. What version of IE or Firefox are you running. Also can you please paste the specs of your PC, what is CPU speed, RAM, etc.

Check your internet connection, check for the latest version of flash and other java plugins get the latest update for them and web browser.
This is just common problem arise due to internet network connection problem.
But once done you can watch full video without any stop.