Check that the switch on the lens (not the body) is set to auto focus and not manual.
Remove the camera battery and put it back in.
Put the camera in full-auto mode and aim at something directly in front of you (make sure it's the object closest to you). If the camera does not lock on to that object then something might be wrong.
Try using the focus point that does light up to focus on a particular area and see if that's in focus (the rest of the picture may be blurry). If it is in focus, then at least the auto focus is working on that focus point.
Try another lens and see if you have the same problem.
Put the camera in P mode.
See if you can change the focus point by pressing the button in the top right-hand corner and then the arrow keys next to the screen.
If all that fails, try updating the firmware.
If still doesn't work then have the body serviced.