In Windows 7, not all icons appear all the time in the tray by default. To modify this, type "tray" in the start menu search box and select the item accordingly. Once the tray icon appears you can then right click it as desired.
Control Panel\All Control Panel Items\Notification Area Icons
To force guide update in Windows Media Center:
A) Type "Media Center" in the start menu search box. Open Media Center.
B) Navigate to Tasks>Settings>TV>Guide>Get latest Guide listings>OK