Mouse menu: Contextual->Join Ctrl-a
When using a function that asks for a point, e.g. line creation, GiD will expect you either to enter a new point (the cursor is a cross) or select an existing one (the cursor is a box). To change from the first mode to the second, click the Join button in the Right buttons menu or the Contextual mouse menu, or use the shortcut (Ctrl-a); the option will then change to No Join. Simply select an existing point to pick it. (Ctrl-a) switches from Join to No Join and vice versa.
Note: Be aware not use capital letter (Ctrl-A) will not work.
The special options FJoin and FNoJoin force GiD to change either to Join mode or No Join mode independently of the previous mode.