I cannot see any videos in YouTube?

I have a broadband access to the internet. I have done speed tests with good results (>12Mps) and tried with different computers but I cannot see any videos in YouTube. I have recently installed Flash Player 10. What should I do?
Sometimes I try to download a video using “a-tube-catcher” but it stops. Then I press “pause” and “resume” and it starts again, downloads around 1MB and stops again. Doing this several times I finally download the video (but, still, I cannot see it directly in youtube.com).