That is definitely a weird problem. Did you try to go into the quick menu and change the settings there? Those should be adjustable with a few combinations of knobs and dials.
If this does not work, try resetting the camera to factory defaults.
This is an option in a settings or gear menu, toward the bottom.
Resetting to factory defaults wipes any custom settings ans sets your camera back to how it came from canon. This does wipe your custom button settings (C1, C2), so keep that in mind. Also, make sure your data on your SD (or CF) card is backed up before resetting.
Also, If the camera starts working well again, make sure to start the camera off right with an in-camera formatted media card. Make sure to backup your photos and videos first! A lot of cameras develop errors if the media card is not formatted from within the camera. A windows or mac format will not do.