When you connect an additional monitor to your computer, the Start button and taskbar are located by default on the primary display—typically, your computer display. If you want the Start button and taskbar to appear on a different display, you must designate that display as the primary display.
To designate the primary display
1. Open Display Settings by clicking the Start button , clicking Control Panel, clicking Appearance and Personalization, clicking Personalization, and then clicking Display Settings.
2. On the Monitor tab, click Identify Monitors.
The display that is identified by the number "1" is the primary display.
3. Click the numbered icon that represents the display that you want to designate as the primary display, and then select the 'This is my main monitor' check box.
4. Click OK.
5. When prompted to keep the settings, click Yes.