Hi!
Here's some basic troubleshooting information from Canon:
""Err 40" indicates that a malfuction related to the power source has been detected. Please follow these steps to attempt to resolve the error:
- Power down the camera.
- Remove the lens, battery and memory card.
- Let the camera sit for 10 minutes.
- Use a soft microfiber cloth to clean the contacts on the battery and inside the battery compartment.
- Reinstall the battery.
- Power the camera on."
If that doesn't work it might be more serious component issue.