I think I might be having the same problem. Did you figure out a way to fix it with out sending it for repairs?
Sometimes when I turn on my T3i, it just doesn't come on. It's like as if you were to power it up with the card or battery door open. Power comes into the camera, but it's blocked from Turning on.
The reason I believe that power is actually coming, is because my lens responds when I stick it on. I have a Canon 28-135mm, and if you've ever used this lens, you've probably noticed that when you stick it on the body, it seems to fire up the IS for a second. It just makes a little clicking sound what I believe is the Image Stabilizer. Anyway, it does this even when the body is doing it's little "play dead" action. Even when it's having the problem and the body isn't turning, the IS still fires off when I stick on the lens. So this is why I believe that it that power is coming in from the battery, but the camera isn't coming on as if it thinks one of the doors is still open.
When this happens, I've tried opening and closing the doors repeatedly. Pulling out, and reinserting the card and battery. Using different SD cards and batteries.
Then somewhere along the way randomly it will just come on. Then it's good for awhile and 2 days...A week... Maybe a couple months down the road it will do it again. Seems to be completely random when it pulls this stunt. Pretty irritating though because I'll pull out my camera to grab a shot and.....it doesn't come on. You can understand why this would get in the way.
Anyways.... All that to say, have you figured anything out?
Where majorblunders said "The camera will start up w/o the SD card in place, but must first remove and replace the battery, after removing the card. Only then will it start.." This seemed to be the case for me also. If I take the card out, and replace the battery, it will start up, but that's still about useless because I kind of need a card in there to take pictures..
Cheers.
