I just happen to know the answer to this question :) so I will post the info here and hopefully someone may find it of use...
the E18 displayed on the LCD is an error code which means the zoom lens is stuck or obstructed when trying to extend. This is a common problem with many Canon compact digital camera models.
you can read more about this error code and a list of many of the cameras affected on this webpage: www.e18error.com
one possible cause for this error condition is something obstructing the tiny geartrain that operates the zoom lens (dirt, sand, etc). It may be possible for you to recover from this error by dismantling the camera and dislodging whatever is obstructing the lens or lens geartrain. Sending the camera in for professional repair will probably cost you more than buying a new camera, so it's worth your while attempting this repair yourself if you're up to it.
several of the Canon digital cameras I've seen are constructed in a similar manner and luckily use screws to hold the case together, allowing for disassembly.
over in the Teardown section here on ifixit.com, I've posted pictures of the steps required to fully disassemble a Canon PowerShot S500 digital camera. Even if you have a different model Canon camera with an E18 error, you may find these photos give you an idea of what's involved in the repair.