4
I would run a file check first, to make sure that you have all the right files.
After that, I am not sure. You might have problems with a theme. If you use a custom theme, you might switch to the "default" theme.
You might also have conflict with some other block and module, which missed some HTML/CSS tag, and is causing this block to misbehave.
I normally deactivate other modules when I am testing, to make sure that there is no conflict.