Try cleaning the contacts between body and lens. Use isopropyl alcohol and a clean rag to wipe them. Also check the corresponding "pins" in the camera, which are spring loaded and should give a little but pop right back into place under light pressure. Of course, be careful to keep off the lens optics and camera mirror when working around them.
You also might do a reset of the custom functions and factory reset of the camera, so see if you've overlooked something that's set incorrectly. You'll lose all your personal settings doing this, of course.
Finally, if neither of the above help, you might "reboot" the camera. To do that...
1. Turn the camera off.
2. Remove all the batteries, including the smaller date/time battery that's in a drawer on one side of the main battery compartment.
3. Turn the camera on.
4. press the shutter release button once. The shutter won't fire, but this should immediately drain any remaining power in the camera's circuitry, forcing it to do a complete reboot.
5. Turn the camera off, reinstall all the batteries, and then turn the camera back on.
6. Check the date/time... if it needs to be reset, you got a proper reboot. If not, repeat the process. If this still doesn't reboot the camera, repeat but instead of pressing the shutter release button let the camera sit for about an hour, to allow remaining power to drain off slowlly.
If you get a proper reboot and the camera still doesn't focus the lens properly, you might try reinstalling the firmware. Download a fresh copy from the Canon website and follow the instructions carefully.
If none of this works, and it's not guaranteed it will (but all are things you can easily try yourself and are free to do), I'm afraid you'll need to have the camera looked at.
Keep us posted.
***********
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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