On the Droid 3, there are four modes your phone can attain while connected to a PC via USB,
1. PC Mode
2. Windows Media Sync
3. USB Mass Storage
4. Charge Only
The update may have forced you into the 'Charge Only' mode.
Fortunately, this is easy to change.
1. First, and most important, use a USB cable that is known to work with the data. Some third-party USB cables do not work as the data pins are not as needed. If you use the USB cable that came with the phone you will be fine.
2. Plug the USB cable into the computer
3. Plug in the micro-USB connector to the phone, make sure it is connected properly.
4. Pull down the Notification area (at the top of the screen) and tap on the USB Connection symbol.
5. Select the mode you need, most likely it is "USB Mass Storage."
6. Tap OK
Your Droid 3 should now be recognized.
Good Luck,
Bob