Im getting a simelar problem, I cant see any Youtube videos or images on sites such as www.ikea.com. I can see the images, but not the ones which has the option to enlarge.
I guessed it was something to do with Java but I have all the right boxes ticked, have just re-downloaded java and the adobe player thing from the link on youtube.
And now Im out of ideas. I tried the smae pages on Ie (I use FF) nothing happened there too.
EDIT: I has solved the problems. I made sure that everything was updated (java stuff, adobe stuff err shockwave player etc) and i hit ctrl-F5. Then it worked.