Do a reset of the camera. Menus, tool, clear all settings and clear all custom settings. Make sure you have a known good battery and a good top quality SD card. That's about all you can do.
Top quality SD cards and batteries do not come from Dollar General or Amazon. Always good to make sure the charger is actually charging too. Do the reset first!
Just realized... Subject states 70D, first sentence states 77D...
Which is it?
If its a 70D and nothing changes after the reset and checking the battery is good, I might suspect the PCB.
Canon U.S.A., Inc. | Product Advisory Detail Page - Does not apply to 77D