Why does video on youtube keep freezin but the sound keeps going?

I have an hp computer with comcast internet yet when I go to watch videos on youtube, the site freezes out of nowhere lots of times except for the sound. If anybody has any solutions please comment!i have superantispyware, malwairebytes, avast free on my pc. i tried scaning with those three nothin worked, then i deleted my accountand made another one, used crap cleaner to clean registry, the default settings not advanced,, still youtube froze out on me and i have to manually click power button to restart computer
what i mean is i can hear sound, but the screen is frozen, and only see mouse

i went to task manager and checked cpu usage and it changes from 0-3 percent then restarts itself so its between 0-3. it says physical memories 26 percent and processes 73. dunno what that means. lemme know yall if u wand me to check other rthingz