Was working fine one day, battery grip attached... pulled it out a couple days later, turned it on, and... nothing. Swapped batteries in the grip, nada. Put in a set of AAs... nada. Pulled out the battery grip, replaced the door, tried all three batteries in the camera... nada. Charged all three just to be sure... nope (two of them took about 1 minute on the charger to show as fully charged; they were barely used since the last charging).
Following various google searches, I've tried cleaning the terminals on the batteries (haven't got to the contacts in the camera yet, but I doubt that's the issue as it doesn't work with the BG either), pulled out the backup battery, and replaced the backup battery. No joy - not a peep, not a flicker. Removed and replaced the CF card a couple times; manually operated the interlock switches on the CF and battery doors... still nothing.
Short of sending this thing off to Canon, can anyone suggest anything else I can try??