! System error

When your camera shuts off by itself, it has detected an error inside. Could be hardware failure, but also a software problem. So no use of switching it on again. Please when it shuts down again, wait till no memory access light is burning or flashing. Then remove the battery. The best thing before reinserting the battery is to charge it first. But if you are sure the battery is fully charged, wait a few moment before you reinsert the battery. Then when you have put in the battery switch on the camera.
When you remove the battery for a few moments, the camera will have a "cold" start. So the program that makes your camera work, start from scratch. As long as the battery is in the camera, the program in the memory does not change. That is why you should the battery.
If your camera has a hardware failure it won't be solved when you remove and reinsert the battery. If the switching on and of occurs while zooming, it could be the lens mechanism has a problem with the gear or motor. If this happens, you should visit a service centre, or buy a new camera.
Then it could be the battery is charged, but not powerful enough to do all tasks. If the camera detects the voltage is under a certain level, the camera also shuts down. If every time the flash has to charge, or the zoom or AF motor needs to work, the camera shuts down, it could be the battery is on its end of life. But for that you should look on the display. Most cameras do have a battery level indicator.

Please check if the lens can move free. If there is any obstruction, it will stop and the camera will give an error. Also never try to stop the lens from moving.
Start over again. Remove the battery, charge it. Place the battery and the memory card when you are sure the memory card is not in the locked position. Then close the battery door carefully, so the door is locked correct. Then switch on again.
If the error comes back, perhaps the lens is blocked inside (broken gear or something like that) you have to contact the service centre.

When showing busy, most of the time the camera detected an error, but can't find out what is causing the error.
Try the normal "reset" method as follows:
Like a cold boot for a computer, the camera can be "rebooted"
follow the following steps:
Switch of the camera and remove the battery.
Remove the memory card and the lens. (if possible)
Recharge the battery. Wait till the indicator on the charger indicates the battery is fully charged.
Check all contacts, if they are clean and shiny. Contacts (from battery and memory card, only to be cleaned with a dry cloth or cotton swab(s).
Reinsert the battery, reinsert the memory card and re-attach the lens.
Then switch on the camera.
If this does not help, contact a certified Canon repair centre.

This is probably THE most common failure among digital cameras. There's a halfway chance of fixing it yourself, described here: http://camerarepair.blogspot.com/2007/12/fixing-lens-error-on-digital-camera.html

Lens errors (E18 errors on Canons) are fairly common. Usually it's sand or grit interfering with the lens extension mechanism. Or the camera's been dropped with the lens extended. Or the camera has been powered on, but the lens had been blocked preventing its extension. Or the battery ran down with the lens extended ...

Here's some things that you can do to try to correct it. They only seem to work for less than 50% of the lens errors, but if the camera is out of warranty, they're worth a try:

http://camerarepair.blogspot.com/2007/12/fixing-lens-error-on-digital-camera.html

Hello,

Will the lens extend when turning on? , can you see any message on the LCD? it is possible there could be a system error or lens error (lens error if jammed all the way in closed position, usually makes the camera shut off right away)

Are there any error messages on the LCD display?

Will the camera lens stay out when the camera is turned on?

Can you still take a photo/flash/sound without seeing the photo?

If the camera will not turn on even with a fresh set of batteries it could have a system or lens error in the camera.

a possible lens jamb when closed and the green led on top comes on then shuts off after the lens attemps to extend but cant.

WE WENT TO THA BEACH AND TOOK SOME PIC AND LATER THAT DAY WHEN WE WENT TO TAKE MORE PIC IT SAID LENS ERROR RESTART CAMERA BUT WE DON'T KNOW HOW TO RESTART THE CAM

Ok everyone.......if your light is blinking while it's charging that means you have a battery error and need to call techincal support and they can possibly replace the battery for you if it is a certain model and within their time frame of replacement.

Usually beeping and then shutting back off means that the lens has sustained some kind of damage and it is just a matter of time before "lens error" shows up on your screen. The only way I know to fix that is to send it into repairs or an authorized service center if you are out of warranty.

Use the audio-visual cable that came with your camera and connect your camera to your TV.  Now turn-on your camera and switch to "view mode", e.g., to see a already taken picture on your LCD.  You will not see anything on your LCD but may see an image on your TV, even if the image is "F18". 

I used the above trick to clear an F18 error on an A75.  Right now I am trying to get the camera to focus properly, but somehow the above cleared the F18 error.

If the above does not work, try connecting your camera to your computer's USB port using the other cable that came with the camera.  Your camera will want to be on, and in the "view mode".  I have read that this trick can reset an F18 error.

Good luck.  At least it costs zero to try these two tips.