I have been using a LXDE live cd and was able to watch all you tube videos and also the BBC I player but after installing LXDE and updating no videos will play. I do not get any error messages. My system has a Nvidia FX5200 graphics card.
Any help would be appreciated.
Got the same video card you have and experience no problems in play back with smplayer or vlc.
Have you tried running the playback application you use in a terminal? If not, please do so and copy and paste the error message you get in the terminal.
I'd also advice to install task-multimedia from the repos, which should provide you with most codecs needed.
Let us know how it goes.