can't move block order or menu items, or anything...

for some reason the drag-drop functionality of the menu items or blocks doesn't work.

When I click on the plus sign in front the line turns yellow, however, it doesn't work dragging.

I tried different browsers and even different computers, the behaviour is the same.

The only 3 extra modules I installed (because I need them) are internalisation, language icons, and module filter. Is there an incompatibility with any of these? 

or?

How do I fix this issue? I cannot nest menus either because of this.