Flash is not working properly

I can't get flash videos or flash-enabled sites to work. I've installed and uninstalled adobe flash player numerous times to try to fix the problem, but nothing has worked. I've searched the internet and I haven't found any solutions.

If I go to youtube and play a video, I can hear the audio, but not the video itself. I can only see the video if I view it at full screen. Otherwise all I see is black or a frozen buffering symbol. Flash animations on websites won't work either.

This has become very frustrating and I would like someone to help me fix this problem.