Youtube keeps freezing

Do you have the latest version of Flash?
http://www.adobe.com/support/flashplayer/downloads.html

You can see your current version here.
http://www.adobe.com/software/flash/about/

Make sure you have the latest video card drivers.

The reason i recommend this is that Flash(used on youtube) can make use of your video card to help accelerate the video now, but sometimes older drivers do not work.

AMD?
http://support.amd.com/us/gpudownload/Pages/index.aspx

Nvidia?
http://www.nvidia.com/Download/index.aspx?lang=en-us

Intel?
http://downloadcenter.intel.com/

Failing that, you can try to turn hardware acceleration off to see if it help. You will use more cpu power, but may be able to see your videos.

http://www.macromedia.com/support/documentation/en/flas...

If you need a flash site to disable hw acceleration, go here again. just right click on the Adobe Flash Player animation on the side that says it is installed.
http://www.adobe.com/software/flash/about/

i got windows 7 and integrated graphics x4500 as a video card. does this give you an idea of the problem?

Intel has a auto update for its graphics chips. I have not used it, but it may be the most easy way for you to get the latest driver for yours. EDIT, just tried it, just installs a small java program, then searches for drivers. Seems harmless. Like Intel would have anything bad on there own site.

http://www.intel.com/p/en_US/support/detect/graphics

Failing that, try to turn off the flash hardware acceleration.