T3i manual mode failure

[OnacAemm]

T3i  works ok in all auto modes and all manual mode when in live view but fails in all manual modes when not in live view.  

Mirror flips up but doesn't return for 20 seconds or so and no picture is recorded.    

Used to work well in all situations, suddenly developed this trouble.  Appreciate your help!

[hsbn · Accepted solution]

You have mirror lock up turn on. With Mirror lock up, the first press will flip the mirror up, then the second press will take photo. If you only press once, the mirror will flip up, viewfinder goes dark, and it will release after few seconds. In liveview, mirror is already lock up so this is not applicable.

[OnacAemm]

Whoops, I found I did have it on as you said. No idea how it happened but I am very grateful for your help and to get my camera operation back to normal. Thanks!