PowerZord
It's time to change.
BSODs are notoriously difficult to diagnose, unfortunately. The fact that it seems to only happen when you are watching streaming video makes me wonder if it's some kind of video card and/or driver problem. Try upgrading your video card drivers to their latest version (not a bad idea to do in any case) and see if the problem persists. Do you tend to do anything else video-intensive with your machine such as playing graphical games, and if so, does this cause the same problem?
Also, does this tend to happen right away as soon as you start watching a streaming video from a cold boot, or does it generally not happen unless your computer has been running for a while? If it's the latter, you may be dealing with an overheating problem. Try using temperature-monitoring software such as SpeedFan to check if this might be the case.
Mostly on Videos but after a long time. For example if i'm into half of the episode of Angel it turns off suddenly. I try to turn it on and after trying to load it turns off again. Last year it happened once when I was trying to create a slideshow for a client using a program called Meeve or something.
Usually when it turns off and I touch it underneath it's very very hot.
It happens randomly sometimes twice a day only.. since later on I was able to watch the final episode of Monk on Hulu without problems.