The cameras are fairly rugged and can take a few knocks (they're not that fragile)... but obviously there are limits. So if the knock or drop was hard enough, I suppose it's possible that you've damaged the camera. Does the body show signs of physical damage (did it fall hard enough to damage the body?)
If you are using the Mac's "System Information" utility to check the devices connected via USB then it is important that you connect the camera BEFORE you start the "System Information" utility.
This is because that utility only scans the connected devices when it is started and does not re-scan if devices are connected after starting. There is a menu option under "File" -> "Refresh Information" (or press Command+R) to refresh if the camera was connected after starting.
If the utility does not show the device then something is wrong with the connection (e.g. loose or bad cable, bad port, bad hub etc.). I have gone through a number of external USB hubs with my own Macs. It took a while before I finally found a hub that worked reliably. I would frequently have devices that would show up in the device list when DIRECTLY connected to my Mac, but would NOT show up if connected to a hub (even "powered" hubs). For this reason, if you are having any connectivity issues, please make sure that you are connected the camera directly to the computer.
Remember, there are no drivers needed for the device to show up -- so if it doesn't show up it is not a software problem.
As a backup plan, it is possible to directly import the images from the computer into the computer without using the camera. I think the 40D uses Compact Flash, but you can get an inexpensive Compact Flash reader (I have a Lexar USB 3.0 reader that has both a CF card slot as well as an SD card slot.) This is actually my preferred method to perform imports because direct reading from the card is faster than transfering via the camera's USB connection.
Tim Campbell
5D III, 5D IV, 60Da
