Hi joudy!
Thank you for contacting Canon USA!
You'll want to make sure you have the most current version of the Canon software installed on your computer so that it can communicate properly with your PIXMA MP640. You'll find the software HERE.
Once you're on that page, click on "Drivers & Downloads," then make sure to download the most current driver from the "Drivers" tab, then head to the "Software" tab and install the most recent version of "My Image Garden" (it should be the top one).
If you run into any snags, or if you already have the most current software on your computer, you'll want to reach out to technical support. If you're in the USA, our team can be reached by phone during the week from 10am to 10pm at 1-800-OK-CANON (800-652-2666) or by email at http://Canon.us/EmailCF. If you're outside of the USA, you'll want to head HERE and select your country or region for your support options.