If your computer is still connected to another monitor when you also connect the HDTV, it's possible the two displays are set up in extended mode; where the HDTV is just an extension of your monitors desktop. If you moved your mouse further to the right from your main display, it would appear on the HDTV.
A couple of options here:
1) Change the display mode from extended to clone. This means whatever displays on the primary display also appears on the secondary display. However, I think full screen movies/games only appear on the primary display and the secondary display blanks out.
2) Swap displays. The displays remain in extended mode, but the HDTV now becomes the primary display (has all the icons) and the main monitor becomes the secondary display (only shows the background).
Where you make these changes depends on what graphic solution you have. For AMD Radeon, use Catalyst Control Center. For NVidia Geforce, use NVidia Control Panel. For Intel integrated graphics, use Control Panel --> Appearance and Personalization --> Display (I think).
http://www.tomsguide.com/forum/59495-4- ... -wallpaper