Dimension 8300

My desktop taskbar disappears from its position at the bottom of my screen.  There is no start button, no time display, the desktop screen extends to the bottom of the screen..  Right clicking in the taskbar area does not open a window to reconfigure.  Higher up the page in the icon area it is possible to right click to  open a window to work with the icons (refresh, rearrange, etc.).  It is possible to restore the taskbar by rebooting, however it disappears after a while.  Any suggestions very much appreciated.