First time building my own computer, i7 2011 Chipset, 12GB RAM and a Zotac 560 ti GPU. I can watch videos but 8/10 times it will freeze part way through playing and then I have to reset it, Graphics drivers are up to date I can't think of anything else.
If you are using the latest nVidia drivers, go back a few. The latest drivers are horrible with video playback, especially online. My system would lock up almost 100% of the time on any streaming video till I downgraded to an older driver.