This is rare, but is generally a LP-E6 battery problem.
- Please plug in the USB cable and see if that will power the controller, or try a new LP-E6 battery. The LP-E6 Canon batteries contacts can become worn or contaminated.
- Alternatively, remove all power (usb and battery). Then, hold down PWR+SET... keep them held down, whilst inserting the battery. Does it power up? If so, upgrade firmware.
Please try these steps and get back to us.