Though there may be an alternate reason, It sounds as though you may be experiencing a failed CCD image
sensor with your camera.
Try pressing the display (DISP) button on the back of your camera several times to see if your image returns at any time. One of the three display modes is "off" to preserve battery life
. Your problem may be as simple as inadvertently pressing this button into the off mode.
If that doesn't work, try doing a reset and then removing your batteries
from the camera for a few minutes, reinstalling them and turning the camera on to test the LCD screen
If your screen is still black, but you can clearly see pictures taken previous to the problem, and you can clearly see the menu system
when you press the MENU button, then you likely have the CCD sensor problem. Contact Canon Tech Support
at 1-800-828-4040 to have the camera repaired.
Hope this helps.