If your C640 is still under warranty, just call Dell and have them send out a tech to replace your keyboard. The exact same thing happened to me while my C600 was still under warranty (Complete Care plus standard 3-year business), and they replaced it with no problems and no questions.

I have the exact same problem, my D and E key were knocked out when I dropped a pocket dictionary on top of my keyboard. I replaced the E key without problems, but when I attempted to replace the D key, the little plastic scissor hinge that connects the key cap to the keyboard broke into two, and I couldn't replace it. Unfortunately, to make matters worse, I was abroad in Spain for the year when this happened, and didnt take care of the problem before my warrenty expired. Now Dell support says the only option is to purchase an entirely new keyboard for 45 something dollars. Not only would replacing the entire keyboard be more of a technical hassle than snapping the key back into my perfectly functional current keyboard, but 45 dollars to fix a problem that is caused by two cent plastic piece is REDICULOUS. Is this for real? If it is Im amashed of Dell and the lows they will sink to to weasel money out of their customers. Has anybody had success fixing such a problem without having to purchase an entirely new keyboard?

Search ebay for your keyboard...I've seen them go for as little as $10. Replacing a keyboard is VERY simple on a Dell...simply unscrew the keyboard screws from the bottom of the machine and the keyboard pops out. It's connected by a single cable connection that is simple to disconnect. You can also look at the Service Manual for your model for help, but don't be too intimidated by it...replacing a keyboard is nothing compared to trying to replace, say, the lamp for your LCD display, or the speakers, etc.

Just something to consider.