why every time i watch youtube video. sometimes it will be pixelated..
Does your lappy have the "optimus" technology from nVidia? Because sometimes, when the nVidia card doesn't do the decoding, the integrated intel does it or just plain software decoding... And it doesn't look good most of the time. You have to click the "use hardware acceleration" when it's a flash Video. If it's not and it's HTML5, then u're on the hands of the browser's API to use HW acceleration. Are you using FF, IE, Opera or Chrome to watch the vids? You could try Chrome or FF and see if it happens.
Telling you that from experience and what I noticed. It could be another reason though, but nothing else comes to mind.