I use to have black screen when am watching video

it's a problem with a video codecs
try to install Klite ful version from here
http://www.free-codecs.com/download_soft.php?d=5318&s=775
then when u install it choose from the options "Lots of stuff" then complete installing
when ur isntalling finished then open any video file through Windows Media Player or click "right click" on any video file then select open with "Media classic"
and hopefully it will work