Does the Quick Control Dial (Canon's formal name for it) let you change exposure combinations when in shooting mode? Does it let you move through the menu options? If it only lets you move through the menu options, the problem is more likely with the QC Dial On/Off switch. If it also lets you set exposure compensation in P mode, or aperture in M mode, then you've got a weird problem.
Canon should still be able to repair that - and it'll certainly cost less than a new camera. Or they might offer you an upgrade to a newer model through the Canon Loyalty Program.
Just in case you don't have the manual, you can download a copy here
. If you don't have the latest firmware version (1.04), it's available here
, and just might help with your problem (not that it addresses that situation, but a fresh firmware might overwrite a random glitch in yours).