Shutter won't fire when using rear screen

One of my little seasonal rituals is to take some photos of the first daffodils that pop out in my yard to celebrate the coming of spring. Now that I'm in my 60s, getting down on the ground to compose those shots, or for any other reason, and back up again, is becoming increasingly difficult, so now that I have a camera with a flip-out rear screen, my EOS T3i, I decided to give that a try in lieu of the optical viewfinder. I've never been one to shoot with the camera at arm's length, so in the ten months I've owned this camera, I'd never before thought to compose my shots on the rear screen. After activating the screen with the button to the right of the viewfinder, I was able to compose, and when I pressed the shutter button, the lens focused and stopped down, but the shutter wouldn't fire; however, when I turned the screen off and resumed using the optical viewfinder, the shutter worked fine. Did I miss a step, or is there something wrong with the camera? I'll admit I'm nowhere near mastering all of the camera's functions, and on my EOS XSi, I couldn't even find a way to activate the rear screen to compose a shot. Also, I only tried this with the 18-55mm kit lens, so I may try a different one today, just to eliminate that possibility.

 

So, I tried it a little while ago with different lens and everything worked fine. I then put the 18-55mm kit zoom back on, and it also worked fine. Not sure what the problem was.

 

So, I've continued to look at the XSi, for which I do not have a manual, and the only logical place to switch between the optical viewfinder and the rear screen is the 'DISP' button to the left of the viewfinder, but it doesn't work. Pressing it just turns the rear screen off. Pressing it a second time turns it back on in the data view. This isn't terrible, given that I use the optical viewfinder 99.9 percent of the time, but it would be nice to know if the camera is working properly and if that's not the correct button to put the rear screen into viewfinder mode, what is the procedure for doing so.

 

Okay, I managed to source a PDF of the manual online and after perusing it a few minutes, I found out a few things:

1. The function in question is called "Live View", who knew?
2. Accessing Live View requires digging through the menus to enable it.
3. Once enabled, it is toggled on and off by pressing the SET button.

The good news is the camera isn't broken; I just didn't know the above procedure. Frankly, it's quite a counter-intuitive arrangement, or at least counter to my intuition. Obviously, it made sense to somebody at Canon, but to my mind, it would have made much more sense to assign that function to the DISP button and have it enabled by default: Data view active by default, one press to switch to Live View, a second to turn the display off, and a third to return to the data view. It also does not make sense to me why Live View isn't available in the Basic Zone shooting modes.

Will any of this make much difference in how I use the camera? Probably not, as I shoot almost exclusively with the optical viewfinder, and I don't see that changing. But it's nice to know how to access Live View on the rare occasions when I might decide I actually need it.