Insert Link doesn't work (wp 3.5)

Hi all,
I am using the latest version of wordpress (i.e. 3.5) and the insert link function doesn’t work. When I click it nothing happens.

This was working fine before the latest update … does anyone have any pointers as to how to resolve this?

(All plugins are deactivated)
Unfortunately I don’t have an IT background so please keep it simple…

Thanks so much!
Cheers!