Franco,
Go ahead and ESC out of what you are doing so the dialogs close. Type
LANDFXDIALOGRESET into the commandline to restore the default locations of all dialog boxes. Then try going back into the plant block selection and see if this fixes your issue. If you are still having trouble, please send in a screenshot of your issue so we can see what exactly is happening. Thanks!
Unable to See Dialog Box, Window, Panel, or Manager, and CAD May Appear to Freeze