1. Have you tried to take a few shots that are manually focused and see if they come out sharp? Use a tripod if possible. If you can't get a manual focus shot to work, there's got to be a some internal problem (if all contacts are clean).
2. Have more than one lens? If so, does the problem occur with each lens.
3. Clean contacts on all lenses and camera body.
4. Does the problem occur when using every mode: P M A S??
5. If you've cleaned all contacts, and the problem exists irregardless of what mode you use or lens, than it's time to send it in to Canon.
Or....there's some great new cameras on the market!!!!