Just to check - are you seeing all of the desktop, or just a portion? If you maximise a window, do you see the minimise/restore down/close controls at the top RH corner, and the status bar at the bottom?
Do you see the whole task bar along the bottom - from the Start button to the clock in the system tray?
Do you have a flat-panel or CRT monitor?
Do you have the correct monitor driver (as distinct from the graphics card driver)?
Have you inadvertently set up a 2 screen display, with the mouse scrolling correctly to the 2nd monitor (that's missing)?
SD