I have a Rebel t3i camera. Yesterday I went to use it and the lens was fogged. After wiping it off, it worked for a few pictures but then the shutter became very slow and the pictures became blurry. I only use the manual settings (Landscape, portrait, sports, etc). I tried it again today and it still sounds as though the shutter is working quite slow and the pictures are terrible!
I switched lenses and the result is the same.
How is the view through the viewfinder? Is it clear and is the lens focusing properly?
Try placing the mode dial in the full auto setting and take some test shots to rule out other settings that were accidentally changed during the fogging issue.
I don't know how well sealed the your T3i is but it is possible that the mirror and sensor were also fogged when the cold camera and lens were introduced into a warmer/humid environment and any debris/film buildup on those would have been made worse by their moisture exposure. It may need to be cleaned at a reputable dealer location. Although the sensor can be exposed for cleaning (instructions are in the manual) UNLESS you are very careful and skilled it is easy to damage this expensive part so if an examination reveals that the mirror or sensor needs cleaning I would use Canon service for this step.
A good guess is whatever fogged the lens also fogged the Rebel. I doubt Canon services the T3i any longer but you might try calling and see. You can try all the easy stuff first. New battery, charger, SD card, resetting the camera to factory, etc.
"I only use the manual settings (Landscape, portrait, sports, etc)"
These are not 'manual settings', BTW. Manual is set with "Manual mode" on the dial. The camera sets nothing then.