Hi, I have a Canon T2i Rebel. When i put the camera in "M" (totally manual), the image doesnt appear in the LCD screen. Everything else works fine in the monitor, but it is as if the lens where...
That's great news, so let's write it up as a solution so that other people who search on here find the right information!
So it appears that the Canon T2i when in manual mode (M) remembers whatever settings you play with, and that these settings are remembered across power cycles; in other words, turning the camera off, or switching to auto before going back to manual does NOT put the settings back to a default.
This gives you the opportunity to set choices that make the screen view totally white or totally black, and unless you realise what you did, you can fear that your camera is broken in some way. At first, I thought this was a user interface flaw, but at least with the screen black or white, you know which way you need to go to get your picture back! The settings that affect brightness are Shutter Speed, Aperture Value, and ISO Rating. They are accessed in manual mode with the thumbwheel, alone, with Av, and after pressing the ISO button, respectively.
One more little bit of trivia: when in manual mode if you don't have live view on, when you half press the shutter, a little indicator comes up on the exposure scale, so that you can see how the settings you've chosen are going to come out.
P.S. I noticed that there was a forum especially for your camera, you might like to join it, it's called t2iforum dot com.