Are the batteries fully charged? Low batteries can display photos, but may not have enough charge to snap a shot.
Are you using flash? If the batteries are low, it may take some time for the flash to charge up and display the scene on the screen. The screen will stay black until the flash is ready.
Are you outside on bright sunny day with polarized sunglasses on? Try without sunglasses on if this is the case.
Has the camera been dropped at all? Even a soft drop can loosen up the ribbon cable that goes to the LCD screen.
Are you able to see the menus? If you can, try a camera reset to defaults in the tools menu to see if that clears it up. You may have accidentally changed a setting that turned the screen when shooting. If not, remove the batteries for a few minutes then press the shutter button for a few seconds. Reinstall the batteries and see if that cleared it up.
If none of these work, you may need to send it in for repair. You will need to decide if it would be worth it or not if it is out of warrranty.