Camera doesn't focus

You can try restarting the camera several times to see if the error clears. We get this often. It may have gone out of alignment off the rails slightly since dropping it has knocked the lens out of alignment.

There's an entire website devoted to this. In a nutshell, Canon E18 error happens when the lens gets stuck while trying to extend. The camera will beep a few times and the LCD will display a little E18 in the lower-left corner. The lens gets stuck in the extended position, and refuses to move either to focus the lens or to retract when powered off.

If your camera is still under warranty, the best thing you can do have Canon should fix it. Warning though, they may nail you for repair charges due to impact damage.

If your camera is out of warranty, or if Canon refuses to repair it for free, the one thing you can try is to If you gently, and I do mean GENTLY push against the lens with the PALM of your hand as you turn it on, it may cause it to depress back into the camera. If that doesn't work, and you can't reset it or turn it on/off several times, then you may have to send it in for a repair estimate anyway.

Be advised, however, that if it's out of warranty, it may cost more to repair than it is really worth. The rule of thumb is that if the estimate for repair is north of 50% what you paid for it, you're better off taking that money and buying a newer and upgraded model.