widget page not working with wordpress French version

wordpress 3.5 (french version)
theme twenty ten 1.5
I want to update widgets in my sidebar. I haven’t made any change on the side for a long time, so I don’t know if the problem is recent or not.
I can’t move or scroll widget area in the widget page to make some updates. I can’t scroll “screen options” or “help”

I don’t have this problem with my other blog using wordpress 3.5 (US version) and twenty ten 1.5. The only difference was that recently I tried and activated different themes for this english version but finally I switched back to my former theme twenty ten.

I tried to activate a new theme for my french blog. But even with a new theme I meet the same problem with the widget page. I switched back to twenty ten but no change. No item on the widget page will budge.

Thanks for your answers.