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Hi! My name is***** am the expert who will be assisting you today.
There are two micro-switches that will prevent the camera from powering up;
One is on the battery door. The other is on the memory card door.
There are some tiny tabs that engage the micro-switches when the doors are fully closed.
Can you check to make sure the doors (and tabs) are (a) undamaged and (b) able to completely close and fit correctly?
If that doesn't help, try the following trick:
(the video is for a 5D, but the same technique should also work on your 70D)
Please let me know if you have any further questions on this topic and I'll be more than happy to help.
Have a great weekend and stay safe,