Try a hard reset:
Remove the battery
Remove the memory card
Remove the lens
Switch the camera on for a 30 minutes
Switch camera off
But battery back in
Turn camera on
Set the mode dial to M (Manual)
Go to the Setup menu and clear all camera settings
Take a shot with out lens
If mirror flips up and back and a clear frame is displayed, put lens on and take shot
If unsuccessful, try the procedure once more. If normal operation is not restored, the camera will require professional service.
You can contact Canon at the link below:
OR The third party service at the following link
Please keep in mind that my diagnosis & solutions provided are directly dependent on the accuracy of your description of the problem. As with any "do it yourself" fixes, success is a "team effort", since I can't see or touch the camera, and relies on the customer's manual dexterity and ability to follow the instructions well. If the "do it yourself" approach doesn't work out for you and you need conventional repair, please let me know.
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