My Canon 60D often does not come on when putting back the battery. So i take a small piece of paper and wedge it between the battery and side case so that battery sits firm in its sitting area.. I have to do a few attempts to get this work. Once the battery is sat right in the battery area it works. Basically the battery does not make good contact with the connectors.
When using sometimes I have re-open battery door and just move the battery a little and it comes back on again after closing the door.
2nd Canon camera I've had that done this..