laptop to external monitor via vga cable not working

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http://askubuntu.com – My laptop is the Toshiba satellite c850-F31Q (with these specs:http://www.laptopdirect.co.za/laptop_specifications.php?laptop=59683)(AMD Radeon graphics card). It is running Linux-Ubuntu-gnome 3 (and Windows 7; dual boot) Urgently need to know how to connect it via VGA to - External LG monitor (works great in Windows). Please could you help. (HowTos)