About a week ago a regular Synaptic update ran in the background. Ever since, when I try to watch a Youtube video (just hitting "play" on the video) the monitor goes black for a moment, then there are just random bars of colour flashing. The only way to fix it is to turn the computer off using the power button and then restarting the computer. I'm using Ubuntu 10.04. It looks like a lot of people have had troubles since that update (red videos, videos that just don't work) but I haven't found anybody with this kind of spectacular crash. I've tried both Firefox and Chromium, same results. Any ideas?