Watching videos on YouTube usually works without much effort, but if your videos come out looking blurry and distorted, you will need to try a few troubleshooting steps. Watching videos at low resolution, having outdated Flash or driver installations or having a defective video card can all cause blurry YouTube videos. Check through possible errors to determine and resolve the problem.
If all videos on YouTube look blurry, but the controls under the videos appear normal, increasing the playback resolution will help. After starting a video, click the number under the video on the right side, then pick a higher resolution number from the popup. Not all videos support higher resolution. If this fixes the problem, set YouTube to default to higher resolution videos in the Playback Setup tab of your account settings page.
A glitch in Adobe Flash may cause videos to display improperly. Uninstalling and reinstalling it will clear out any incorrect settings and ensure you have the latest version. Open the Start menu and click "Control Panel," and then open "Programs and Features." Select each entry beginning "Adobe Flash Player" and press "Uninstall" to remove it. Visit Adobe's website to re-download Flash and install a fresh copy.
Update Video Drivers
Outdated video card drivers may have bugs that cause distorted YouTube videos. For computers with discrete video cards, visit NVidia or AMD's website to download updates, depending on your card's brand. If you use Intel integrated graphics -- common on lower-end computers and laptops -- you can find driver updates on Intel's Download Center. Be sure to download the drivers for the version of Vista you have, as incorrectly selecting between 32- or 64-bit drivers will cause additional problems.
Disable Hardware Acceleration
By default, Flash videos use your graphics processor to run, taking the load off your CPU. If your video card is faulty, it may cause graphical errors in YouTube videos. Open a YouTube video and right-click on the video. Click "Settings" and click the first tab button on the lower left. Uncheck "Enable hardware acceleration" and press "Close." Refresh the page and watch the video. If this fixed the problem, your video card may need replacing, but you can watch videos without hardware acceleration in the meantime.