1- Right click on the taskbar and select properties
2- In the Notification area heading, click the Customize button
3- Click on the “Turn system icons on or off”
4- The first item should be clock. Select on instead of off.
5- Click ok.
Un-check the “Use small icons” option in Taskbar/Start Menu Properties. If set to small, the date is not displayed.
http://www.sevenforums.com/general-discussion/138926-how-show-time-date-taskbar.html